How can a bug that doesn't exist sound like anything?

Signal patched WebP weeks ago.

When I heard about this, I also associated the two. The report talks about link preview generation, so it sounded like someone could put a webp on the social metadata of a page for link previews, and then send it as a malicious payload.

But that would mean any app with link preview (eg. slack, whatsapp, discord) would also be affected...

Nothing in the linked article even remotely suggests that.