[GuB-42]

Etymology can be complicated...

As a French, I have another explanation. The french equivalent to a "dunce cap" is "bonnet d'âne". "bonnet" means "cap" and "âne" means "donkey", so "bonnet d'âne" literally translates into "asshat".

It is probably not the true origin of the word, but it is not impossible either. Also, words can have several origins.

[elevaet]

Multiple origins are probably more common than we think. We tend to be biased to want to see singular causes of things, but language is often a murky soup full of feedback cycles.

In the example you gave, if it is not an origin, it could at least be a lingual context that supports the expression, because it does not contradict it.

Language evolution must be full of nuances like that, that we can barely observe.