Only a few people in history before the telescope and even after knew
for example that the stars were other suns, only much farther away,
or that Earth circled the Sun and not the other way around. Expecting
them to know that those "nebulae" were other galaxies when they didn't
even know the concept of a galaxy existed is a bit much.

I am sure we will look equally clueless when revelations are made about
the Universe that we can barely discern now, such as extraterrestrial
life or the nature of dark matter and dark energy. Hopefully posterity
will not be too harsh on us about that. At least we are attempting to
discover new things and making science-based guesses about them.