The only rational explanation(beside someone hacking Reddit) is that admins wanted to promote /r/Home because of corona-chan so the reddit lemmings will stay home..if that even makes sense(to admins).
The less rational explanation is that Reddit counts some hidden statistic about that sub activity which is unusually high(something like moderator actions) and the mods there implemented a bot that bumps some activity counter every second - it makes less sense because Reddit defining activity mostly from "concurrent users" number(that is around 20-30 in r/home).