"The idea is to talk like a small child or intellectually disabled person"

That's effectively an ignorant description of the entire doge meme.

RationalWiki's "source" for this information is a Reddit post with 6 upvotes and 5 comments. It's remarkable that anyone on hackernews even knew about this.

What is this subculture that watches for any slang to be used by an objectionable group so that it can be proclaimed a cultural characteristic of said group?

Mostly people talking about it, not using it.