It is very easy to make up a plausible sounding theory. The hard part is making sure it has no holes in it. The harder part is proving it. As an example, I'll give an alternative evolutionary explanation for why it makes sense that (some) people can accurately judge others in a short amount of time (I claim no expertise in the evolutionary sciences; this is written as a layperson):

Consider an intelligent social species. When two strangers meet, the ability to judge accurately and to be favorably judged, both lead to better fitness. Lets assume there are situations where intelligence is the dominant quality that is being evaluated. Now if you are intelligent, you want to honestly communicate this, so its in your best interest to aid the judgement of the other person. If you are not, then its preferable to be dishonest and try and simulate intelligence. Now why should this situation lead to a state where (some) people can fairly easily make accurate judgements about others? It seems like the person judging has no easy way of accurately evaluating, but has to undertake the hard task of distinguishing between liars and truth-tellers. But the interesting part is that lying and intelligence are highly correlated, since lying takes more brainpower than just telling the truth. So the people who can fool the judgement of others, don't really need to, while those who need to lie, can't do so effectively. This evolutionary dynamic leads to a state where intelligent people can quickly judge the intelligence of others, because they don't have to worry about other intelligent people fooling them.