It predates the co-opting by the alt-right though.
So does the "OK" gesture. The swastika existed for almost 2000 years, and was a good luck symbol, even in the west, until 1930s. The sonnenrad, the othal rune, the Celtic cross, and the triskele.
P(uses the OK gesture) dwarfs P(is alt-right). Plug it all into Bayes theorem and you'll find that P(is alt-right|gestures OK) must be small.
In other words, you're falling for a manufactured hysteria. One that is designed to make people jump at shadows, level unjustified accusations, and generally make you seem uncredible and neurotic.
The swastika, on the other hand, was used in living memory by an organization that murdered millions of people. Like the toothbrush mustache, it will be generations before that can come back in style.
"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?
Not for any "extremely online" person. Hell iirc, the original honkler subreddit or whatever the hell it was called even made in to mainstream media.
Mostly people talking about it, not using it.