You can call that claw leaf if you want, but if it was, it wouldn't be localized. I see perfectly healthy leaves in that circle except for the lowest fan leaf which is beginning to lose the war with gravity. Think about it, if it had a nitrogen toxicity issue, the ENTIRE plant would be affected, not a couple of leaves. I've seen N claw several times, that ain't it. The dude is watering the hell out of the plant to prevent the roots from drying due to an air stone.
It's possible that it's getting too much Nitrogen, but your diagnosing that out of the blue based on that photo is rather a crap shoot.....
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The one below is an extreme example.
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