It’s fine if people keep it to themselves.. it hurts when they state these assumptions as facts which is a wrong advise for people

Cognitive dissonance is holding conflicting beliefs simultaneously. For example, believing that immigrants are lazy and job-shy whilst also believing that they are taking all the jobs.

What you described sounds more like either a lack of awareness or revisionism (depending on how conscious it is).

There are parallels, though, and I don't like the snark you're getting from other replies here. Both relate to how identity and image drive beliefs. You could even frame the revisionist founder as having cognitive dissonance about what the primary reasons are for their decisions.

No one but you knows how you came to have the wrong understanding of a term.

One way it can happen is by unguided learning only from context, ie you heard or saw the term used and formed your own recognition pattern, without ever consulting a reference to find out if the guess was correct.