I've seen that entire game replayed before and Larry was pretty much making most of that game look easy. When it was obvious that the C's were going to win late, he was so comfortable that he just shot whatever crazy shot he wanted to. It didn't hurt that his teammates were cheering him on to shoot more.
Remember the backstory, though, McHale had just set a franchise record earlier that week and Larry told him he'd break it. Fantastic.