No one knowing where he was is implausible. These folks are like royalty in that they have an army of aides and sycophants around them 24/7.
Secret Service had to know. Not their job to speak out. I’d have to think someone at DOD knew as well, and that there’s a procedure for his absence. But his top aides only seemed to know the tasks they were to take over, not his location. I’m sure they could have found out, which takes time. But this administration, who knows.