^^^
I’m not sure I agree with this advice, even if it is accurate. Pushing air against your belt keeps your body tight through the lift, and when you blow it out you lose tightness. I’d rather be tight and get a headache later than get loose on a big lift.
Here is a thread with Meat’s advice on breathing and bench, and I am pretty sure he advises the same for all the big lifts, DL and Squat included.
In short, I try not to breath during a big lift. If I have to breath, its at the top of the lift.
My .02 cents.