Complete speculation - some decent program said they were booked scholarship-wise for 2018-19, and told him they'd sign him for 2019-20 if he played JUCO ball for a year.
Or - he had mediocre interest due to his limited body of work, and thought he could improve his 2019-20 stock by putting up some gaudy JUCO numbers.
Wherever he went he'd need to sit out a year, so I'm sure playing any level of basketball was more appealing than sitting on the end of a bench in street clothes watching the other guys have all the fun.