They were probably originally based on optical illusions caused by unusual reflections/refractions in the atmosphere. They would have been like mirages that you can’t approach to realize it’s not really an object. Kinda like a rainbow. Biblically accurate angels come from people trying to make sense of seeing light doing weird shit.

Though I bet there was also improvisation of those for some of them. Like “oh if this is possible for angels, they must also be able to do x!”