To answer the last part of your question, they don’t need to think of Lemmy at all. “Lemmy” is a framework, not a social network. infosec.pub is the social network I’m on. I don’t need to know about Lemmy at all (most of us don’t know what powers Reddit). Here we discuss information security and I can also communicate with the wider fediverse.
It doesn’t even have to be lemmy. I can connect to anything that uses activitypub. Mastodon, Kbin, Bookwyrm, Wordpress, etc. using my infosec.pub account.
The lemmy code provided by lemmy team is cloned and then patched (if needed) by infosec.pub maintainers and then deployed to their servers. The code for all intent and purpose is owned and maintained by infosec.pub. Lemmy doesn’t have any real control at that point.
Same with the arsenal example. arsenal.club is a social network about Arsenal powered by lemmy framework. If mufc.club uses another activitypub enabled protocol, the arsenal fan on arsenal.club can view that in their subscribed feed too.
it’s part of their anti-adblock code. without going into too much details, they can instantly find out whether ad-block is trying to do anything on chrome, but on firefox they need a 5 sec delay