Forget the salary -- it is about him being able to receive other forms of compensation without restriction. If he goes to college, then he doesn't get paid until he declares / leaves college to go pro. In other words, no $$$ until April 2019, per NCAA rules.
By doing this, he can get endorsement money, he can sign sneaker contracts, he can receive loans from agents -- all without restriction. Not life altering money, by any means, but enough to float him through the year and elevate his family's circumstances in the short term until he cashes in with an NBA contract. So, in the big scheme of things, the G league salary is irrelevant -- it was likely more about removing the restrictions the NCAA imposes on getting paid, and getting access to $$$ faster in the short term.