“Are we involved in that, as are we a subset of lemmyworld?”
No, since kbin.social and lemmy.world are not only two separate instances, but two different Fediverse applications (kbin / lemmy)… so yeah we’re fine for now.

“but any content I engage with is effectively visible”
I self-host a small Calckey instance and previously self-hosted a Mastodon instance, and something I noticed is that different instances don’t always federate well… So remote messages won’t always show up.
E.g. say I follow Eugen from mastodon.social so I see his posts. For example there are four replies: one from a guy I follow on infosec.exchange, one from a fresh new account on mstdn.social, one from a tiny one-person instance, and one from a suspicious instance that was quickly suspended. I can (most likely) only see the first reply from my instance because the latter three won’t federate with my instance… so yeah that’s completely normal.

“How does this affect us?”
As background knowledge: (some) people are awful. In practice this means that any large, open-registration social media WILL attract difficult people. To solve this, select at least one: 1) close open registration, 2) limit the size of the instance, or 3) be ready to put a lot, a LOT more effort into moderation.
Many for-profit social media, as well as some large Mastodon instances, have to stay open-registration for various reasons, so they have to find large numbers of moderators to do the thankless jobs of filtering out terrible stuff. This doesn’t always work smoothly. Pretty sure lemmy.world and sh.itjust.works were defederated because of this reason: open registration, and mods couldn’t handle the bad people.
Pretty sure kbin.social is still open-registration at the moment? I mean kbin isn’t as popular as the previous two so I assume we are safe now, but unfortunately ernest will have to make the tough decision one day. Jerry from fedia.io probably already knows what to do since he already manages infosec.exchange, one of the larger Mastodon instances lol.