I suspect this guy had planned this for a long time... (maybe not the exact date, but an attempt sometime when Trump was golfing at this particular club) perhaps even before the July attempt in PA. He probably knew the area well, and just because the golf round wasn't on Trump's schedule, there are still likely obvious clues that he's there if you pay enough attention. He learned what those clues were, found his opportunity and went for it.
Immediate 10-cent move toward Trump on Pinny right after.