I am guessing by very dint of the conjecture that flat-Earthers are also atheists.

Herd of cats.

In social media, I have come across individuals that appear to make the terms, "atheist," and, "evolutionist," synonyms. I think that this illustrates the kind of jump to a conclusion that you are talking about as many evolutionists are not atheists. They are expanding a definition to fit what they want to say at the moment.

I`m not

Sadly, we currently live in a society that, by and large, has ceased to think critically and can only evaluate and make sense of external concepts purely in either/or terms. It is very easy to judge or vilify or discard opinions of others if one paints with a large enough brush in the broadest of all strokes. Questions like "Are xxx This?" or "Does yyy That?" are symptomatic of mental over-simplification.

Of course we are all individuals with vast differences. Objectively pondering those differences makes most peoples' brains hurt.

Yes we are