But he is.
Watch him wobbling around while doing those presses.
He is absolutely working his core.
He is stabilizing himself partially with his offhand because he's not strong enough to press the DB without it.
This isn't some secret lift.
If you actually watched the video you'd see him address everything you claim
You'd also see him do standing bb press with 225 with no leg drive or back bend
The dude is precise in every rep of every movement
BTW - who said it was a secret lift.