Most likely scenario is that it is deferred compensation. This was addressed directly in his contract extension that he signed back in 2020. It had to do with him hitting certain performance metrics (women's soccer championship, men's basketball NCAA Tournament appearance).Right, his comment that his W2 says $500k can be true for 2025, but why would the budget list his compensation as $800k+ if it wasn't going to be. If that's wrong in the budget, then they have bigger issues of not being able to prep a budget properly.
It is probably money put into a 457(b) or a NQDC account that Burman won't actually receive until he retires. These funds are often reported on the accounting end because they are financial obligations that are due to the employee even though the employee hasn't actually received them yet. The employer doesn't want to lose track of those expenses and have a surprise financial responsibility when the employee retires.
So Burman might actually only be paid $531k this year, but he will eventually be paid the additional funds at retirement.