The picture says it all (feel free to add free-hand circles):
I had already two different versions of this strange behaviour, having some hours old question in-between the really active ones.
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Just a guess.. "activity" also includes votes, it seems, because if you look at this one
And click through the OP and answerer's profiles, then the new whiz bang reputation page, it shows votes/voted in the last 13-14 minutes.
Tracking through the other questions, any comment or vote seems to also count as "activity".