Pretty standard around here. I prefer 3's, but he may have been going for reduced pellet number while shooting over decoys.
I'm a bit prejudiced because of course in hunting tests all our shots are quite close. 4s are plenty under the circumstances. Somebody one time issued the gunners a box of 2s at a Junior test, and I unfortunately was running the test dog. I wondered why my ultra-reliable older dog was putting down the duck and picking it back up again repeatedly . . . until I took it from her and my hand went right through. Gack. If I'm going to be drawing a bird I like to know ahead of time.
The judges (1) retired that bird; (2) took back the No. 2s and gave the gunners 4s. That worked much better, although of course then we have the wounded birds to deal with. Lots of unintentional humor in a confrontation between a young retriever and a wounded and angry mallard.