I will be very surprised too. I remember that he skipped his senior year BB to enroll early, so it would be at least 4 years since he last played organized basketball. That said, the timing of the switch suggests that at least he believes (it could be a total illusion but more likely based on feedback from basketball staff) that he could contribute beyond the practice squad. Otherwise, as he is not totally buried in the depth chart in FB, he could at least wait until the end of the football regular season to test the water, then make a decision on what he wants to do with his last year of eligibility.
Harris certainly will be behind MAAR at 2G but I don't see him necessarily behind either freshman Brooks and Poole as the back for MAAR. He has a mature 6'4 body and elite athletism, which should at least translate to a more competent defender.