The suspect, whose picture was widely circulated by parents, SFPD, and KTVU (and briefly on SFist before we pulled it soon after publishing) in an effort to track down and question him, was described in the Examiner as “cooperative,” “unguarded,” and “surprised at being the subject of a police investigation.”
His laptop and phone were cleared of anything suspicious. The suspect said he was using his phone to time the pull-ups. (Occum's Razor in action, thankfully.) He was then told to mind the signs prohibiting adults who aren't accompanied by a minor in children's play areas.