It's not a question of water pressure vs. air pressure.
It's a matter of common sense saying that it is a bad idea to tie yourself to and anchor and jump in a lake.
I would think that the problem is the volume of air in the hose. 30 feet of hose filled with carbon dioxide would have to be forced clear of the hose so that fresh air and oxygen could go back down. The lungs can't clear the hose at that depth.
And the hose may have actually been longer, maybe a 50 foot hose, adding to the impossibility to the attempt.
Now, was he smart enough to breath out into the water and only breathe in through the hose? Probably not!