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Or epistemology. Or logic.  We can thank Dewey and the Pragmatists for that.  But I digress. 
While an autodidact (notice the second 'd') is defined as a self-taught person, it is not necessarily the case the reverse is true. 
But we are also talking about connotation and a quirk about English grammar. When you say a person ""is self-taught"", because taught is in the past tense, it gives the impression of being in the past. It is also ambiguous, as people are likely to say/think/ask, ""self-taught in what?""  But if you say a person is an autodidact, it maintains the present tense and does not suggest when the self-teaching occurred.  It also implies a general sense of being self-taught. For instance, I taught myself how to program computers. But I don't go around claiming I'm an autodidact. With Langdon, if you say he is ""self-taught"" and mention his IQ and status as a bouncer, well, that hardly gives a meaningful impression. 
For that reason it's as I stated earlier  an approach to learning. Langan is generally self-taught (or something like that), but more critically, I think, his attitude seems to be ""why should I bother learning from someone who is my intellectual inferior"". That's the impression I got from the video interview. 
Having said that, I assume someone else did call him an autodidact, right? Because if not, then the whole thing is OR. 
 
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