He literally said he put in some ranges in a EV calculator and said we are making lots of money.
"lots"

We must make more when we 3bet to 12bb. Imagine bb wakes up with QQ+/AK. Let's say we have AJs, a clear 3bet spot. When we go to 12bb, bb can 4bet us with his QQ+/AK and we can easily fold, saving us 80% of 90bb compared to the times we're committed by making this shove.

btn is an irrelevance. He's shoving a lot when we 3b to 12bb, and the times he doesn't he faces a half pot shove on the flop before he blinks. Just because btn is the target, we can't ignore bb. He's full stacked and we want to play our range optimally vs him too.

By 3betting 12bb, we also give the bb a chance to flat, and then when btn shoves we can print money by reshoving.

I would be really surprised if this shove is optimal. Profitable? Sure, but if you have AA here, you know it's a) profitable, and b) dumb.