BSD never ever has security issues so kernel updates are never necessary?

That would be a bold claim and one I've never heard before. Hard not to be suspicious of it.

This security flaw is unlikely to be the only security flaw that ever happens to a kernel used by routers.

The point: Consumer routers do not seem to get updates. Ever.

Is that a worry or what?

Google tells me almost none of them run BSD and nothing I've ever heard of, much less seen.

But what do I know about it beyond that?