Who knows if that amount is true. USC is a private school and it doesn’t have to be made public. I would be surprised if that number is correct.
I'd be surprised if it's very far off. As a private school, when it comes to paying coaches, USC is really only constrained by how much boosters are willing to kick in. A lot of boosters are sick of what they have been watching since Carroll left and were likely willing to pay that kind of money (or close to it) to get the program back to standard.
You also have to remember, USC got burned when they hired Kliff Kingsbury and then lost him to the NFL before he even met with the team. My guess is that part of the reason he left would have been more money.
Paying that kind of money should help prevent that from happening again. Of course, the flip side of that is that is that if he doesn't work out, they're looking at a huge buyout.