My understanding of the event:

• 4chan jokes they should pretend the okay hand sign is a white supremacist dog whistle to trigger libs.
• They do and it works.
• Online shitters who's whole personality is "triggering sjw's" pick up on this and perpetuate the joke to continue to trigger people.

Basically people getting mad at a joke caused it to become a real thing to some degree. While not a supremacist symbol it was heavily used by them for a time.