Colloquial English is educated, but still not stuffy sounding. Colloquial is more formal than the way of speaking we would use to talk to our best friend, and doesn't include a lot of slang.
Formal English is both educated as well as stuck up. No one would use this form of speaking while talking, however it is often written. Despite being often written, this form of language is not as poular for witing as it was in the past. Formal English shall never contain slang.
If the bold sentence is in fact As he tells the story he never smiles, and he never frowns",then it is most likely the human foible due to it being an interesting characteristic. We can also determine this answer through process of elimination if we know the meaning of hyperbole, and "funny name".
Hyperbole is an exaggeration and is not normally meant to be serious, and in the case of your summary, I believe this line is meant to be taken serious. This doesn't seem to be a funny name reference, so your only option is human foible.
