This has happened to me three times now, and when I brought it up in #wikimedia-tech, User:Quiddity confirmed it. Basically, we've gone to wikis where we weren't already centrally logged in (for me, at least, always going to a specific page there, not just the main page) and wound up at Special:AbuseFilter. My three were:
Quiddity says he doesn't remember which page he was looking at.
This was apparently my first time visiting frr or roa-tara (or at least the first time that my account was activated there), but I've had an account on hi.wp since January
Setting severity as "major," since this is very unexpected and confusing behavior, and could be indicative of larger problems.