Well perhaps Elisha really did see a chariot of fire and horses, although what we would have seen if we viewed the same event may have been different. So in other words, if we could time travel back to that event and watch it along side of Elisha, he may have seen a chariot of fire and horses taking away Elijah in a whirlwind, but we may have seen a flying saucer beaming him up. We have seen images of flying saucers and other spaceships flying to far away places in space on television and in movies for decades now. Elisha had never seen such things. So his mind interpreted the phenomenon in a manner familiar to him. Chariots and horses would have been what was familiar to him, and the fact that they were flaming denoted that there was something special about this chariot and these horses (the fact that they were flying). In our case, we see something metallic that appears to be mechanical and/or electronic based. Typically UFOs we see look saucer shaped, triangle shaped, cigar shaped, or bell shaped (a.k.a. acorn shaped). Perhaps how we see these objects is partially reflective of what we are conditioned to think they look like, and partially reflective of us recognizing it is something 'special' and foreign to us (which is why we don't see it as just a plane or helicopter). Perhaps if Elisha saw them, he would still see a flaming chariot being pulled by flaming horses. And it's not necessarily that there is a right or wrong way of seeing it. What's important is that it is seen and manifests itself in the minds of those who see it in a way that is understandable to them. In other words, what Elisha saw and what we may see manifests as something somewhat familiar, yet as something special and foreign to us at the same time. And it's not necessarily that the angels/aliens/demons are disguising themselves (though that isn't to say that they can't), but how we see them depends on who we are.
I think this phenomenon may be further evidenced by how people see ghosts. Some people ask the question of how a ghost could have clothes on (the clothes were never alive, thus they can't be 'dead' either). Well, when people see a ghost, it's not that the ghost isn't there, they just aren't seeing it in its true form. Their mind interprets the existence of the ghost in a way familiar to them. Typically, most people only know what a person looks like with their clothes on, so the mind interprets the existence of a ghost as a person with clothes on. I think the same can be said for angels, demons, and maybe aliens. Some people have seen angels in the traditional artistic form of a person with wings and a halo, others have seen them as glowing figures, sometimes with golden hair or apparel, and others have seen them as ordinary looking people that perform some good deed then suddenly disappear. I think in the case of angels, how people see them may be based partially on what a person thinks an angel should look like, and partially on how the angel projects itself. In other words, in some cases an angel may want a person to see it as a spiritual being, in other cases it may just want to help someone out without alarming them or bringing unnecessary attention to itself (such as when they appear as an ordinary person). The same could be said for demons too. Demons have been portrayed and seen as all different types of nasty and grotesque creatures. In some cases though, they may be be seen or portrayed as beautiful and seductive creatures (we also know that demons sometimes disguise themselves as angels of the light). Aliens are typically seen as reptilians, Nordics, or grays (it's been said there are two types of grays, those commonly portrayed with large almond shaped black eyes, and another kind with more human like eyes and features, though still gray and hairless). Perhaps these aliens we see are some type of manifestation of angels and/or demons.
So to conclude, although it is possible for angels and demons to project a certain image of themselves to us, how we actually see them is largely a manifestation of how our mind interprets them. We should also be careful not to confuse a spiritual vision with an actual event. For instance, in the book of Ezekiel, Ezekiel sees a vision of God and a wheel within a wheel. Some have interpreted this to be some type of UFO, but in reality, I think this was a spiritual vision portrayed to Ezekiel specifically. So even if you or I or anyone else had been sitting next to him when he saw it, we probably would not have seen anything. While on the other hand, if we had been with Elisha when he saw Elijah taken away into heaven, we would have probably seen something; whether or not or it would have been a chariot of fire or a flying saucer I don't know for sure. The difference is one is a vision, the other is an actual event that is occurring. While people of today and people of the past may view certain similar events differently, it doesn't necessarily mean that the events themselves are different. We should also be careful not to be pretentious and assume that we are seeing it the "right" way. What's important is not necessarily how it was seen, but that it was seen.