Here's my quick take, without any studies.
If he's getting only .5g/lb, thats 90g of protein = 360cals per day from protein.
say, hypothetically he gets 40g fat per day, that's another 360 cals.
Now, if he's only getting 90g protein and assuming not a lot of fat, he'd have to ingest a HUGE amount of carbs in order to ingest the thousands of calories that competitive swimmers require, to the point that it comprises probably around 85% of his diet. This seems to me to be totally out of whack.
I put some hypothetical numbers down and I got this: 90g protein, 40g fat, 500g carbs. That's only 2720 cals a day.
If he's swimming 20+ hours a week i'm sure he needs MUCH MORE per day.
By grossly limiting one macro, you have to make up for it with the others. And i'm just guessing he isn't getting a ton of fat; therefore he'd have to ingest a ridiculous amount of carbs each day.