350lbs. as the article points out, is not crazy big for a grouper. Goliath grouper fishing vids regularly show fish like this (always catch and release) being caught, and sometimes on hand lines.
ETA: he is indeed standing behind it, but if you look close he is touching a spine on its dorsal fin. So he can’t be too far behind it, and it cannot be too terribly close to the camera. His arm is bent as well, so it is unlike those fish pics where the person has their arm obviously extended in front.
