They have no obligation to offer a playthrough, especially if you didn't ask. Maybe they don't even know about playing through. It may be an unpopular opinion, but I think your behavior was completely unacceptable. Throwing into them, even if you knew they were safe, is a far worse breach of etiquette than making a singleton cool his heels a little bit.
I agree with you here. If you don't ask, they may not know you want to play through. In many solo rounds, I catch up to people and if, I'm not in a hurry, I just throw a few tee shots and slow down my pace.
Even if you "know you won't hit them", all it takes is one bad tree bounce or skip and it could have gotten ugly.