Human memory is exceedingly malleable. Given days, months, years, let alone 20 years, a minor optical illusion can grow into quite a story.
That combined with general misconceptions, cultural and belief predispositions, poor levels of education, drug use and straight out desire, makes eye witness accounts less than reliable.
This is why anecdotal evidence isn't really worthwhile. Certainly not to prove anything as extraordinary as extra terrestrial life and or visitations.