Last year he was on a scholarship contract like most 17-year-olds. The club then offered him a new professional contract (I think last summer, can't remember) but he stalled on signing, largely because the club wanted him to become a LCB but had no real pathway into that position with Gabriel, Calafiori, and Kiwior all in the first team as well as a number of left backs.
Arsenal did not make much of an attempt to change his mind or show him a pathway. He has played 10 minutes for the first team in one League Cup appearance, only been on the bench for 3 PL fixtures, and mainly been with the U21s and trained with them.