To me, sounds 2 things are going on:
No matter how "innovative" they try to make it sound, Dinwiddie is taking out a 3 year loan (well up to 90 loans). Give him 150k now, he'll give you $3,750 a year for 2 years in interest, and in year 3 he'll pay you back your original $150k, plus 40% of his post tax contract in year 3 (divided among the 90 shares). Expect annual returns of 7%-10%. I have to imagine several players across the league have various loans for business they try to start, it's called leverage.
The deeper, and really innovate thing, is he's trying to start (and profit from) the platform where all athletes can take out "loans" like this and these loans can be traded on the secondary market. Now that's interesting.