He didn't lift the sub out of the water, is the thing. He DID accelerate it a fair bit upward, though it took time, and given that he can move at thousands of km through water it seems, he clearly has that much thrust. But once it was moving upward, it breached, like subs can do even when not directed somewhere. It isn't nothing it's just that people were trying to say it was a "hundreds of thousands of tons" level feat, and it's simply not even close to that.
Also, subs weigh ZERO under water: they make themselves neutrally bouyant with ballast tanks.