They do have some of the best fans in the country and sell out their 10,000 seat arena every night. Still, that's not enough to afford him.
They are paying for him in 2 ways, probably:
1. Private donations
2. The university's general fund
Especially because they have no football, basketball is critically important to Wichita State and they probably have a long-term objective to be a Gonzaga-type program, a nationally relevant every year program. They'd LOVE to land a spot in the Atlantic 10 (hey, Creighton's in the Big East, why not) or the Mountain West if they'd ever allow non-football schools in.
Despite what anybody thinks, these universities are filthy rich and can afford to pay their coaches (and players) almost anything they want. Its just that some schools choose to do it and some schools don't.