Articles before names

What I’m interested in now is not easy cases like “the John”, meaning somebody who’s famous for one or another reason. However, I have recently come across a phrase that went more or less like that:

“Blah, blah, blah,” said a surprised John.

I do realize that such techniques are relatively rare in English-language literature (I don’t recall any other examples of it) though I’m trying to understand why an article is needed here at all. After all, names of people are not just average nouns.

It is called ‘reclassification’, I think. The article divides ‘John’ up into several personalities and then chooses one of them as the statement component. It is reasonably common. It happens with proper nouns and uncountable nouns: a subtle beauty, a better Chicago.