I just saw this arrive in my inbox and for a very brief moment wondered if I’d slipped into a tear in spacetime, taking me back a decade when Sam added this.
Probably the topic was bumped or edited, but perhaps the email trigger needs to be tweaked slightly. When you read this without context it’s a bit confusing 
I think the reason for the email is that the topic was moved to Announcements, and by default, everyone is watching for first posts there. The fact that it was moved again later makes this less obvious.
I was confused in a similar case a few weeks ago Preventing notifications when moving topics to announcements category
