Yeah, I think Amethyst is one of the worst clients about connecting to relays that you did not select in your relay list. I think it is going beyond what is expected in the outbox model.
When building your home feed, it should only be fetching top-level notes from your follows' outbox relays.
When showing replies to your own notes, it should only be fetching from your own inbox relays.
When showing replies to other users' notes, it should only be fetching them from that user's inbox relays.
However, as evidenced by all the various relay login requests I am constantly inundated with, I believe it is also fetching notes from the inbox and/or outbox relays of those who have replied to a top-level note, and maybe anyone tagged in those notes, too.
That means you WILL see spam if those users have not been on top of maintaining their relay lists.
