San Diego State gets $15M for new stadium From what I've read about it, the short answer is that this is just hype to solicit more donations and/or some nice starter capital to start getting shovels in the ground.
Long answer is that the finding situation is super complex because the Q is losing money with maintenance right now so the city can think of the act of destroying it as an annuity worth millions per year. They could pass some of that on to SDSU by offering them a sweet deal on the land.
SDSU does expect to take on debt to fund it, but they expect to pay that off with annual revenue from eventual sponsorships. So their up front cash outlay will be a lot less than $250 million or whatever the total estimate is now, and therefore this donation actual does matter a little