The simplest explanation is usually the correct one. I wonder if President Trump playing that course is his usual or if there are many potential courses he plays? If many, it becomes more curious as to the shooter being there at that time unless the shooter staked out that course for an extended period, somehow not being noticed until the Secret Service noticed him.
Didn’t he play the morning after the first attempt? I’d say it’s a safe bet that if he’s in Palm Beach, he’ll likely golf. And where else? The SS is probably quite familiar with the place. Good eyes, spotting a rifle barrel stuck through a fence at 300+ yards.