^^^^ What SK said, I don't see this as a misunderstanding either. You were expecting a "normal" reaction, like "hey, was that message for my Dad? It's actually me here, I have his phone right now".
You didn't even text him, you texted his Dad!! He knows that, well he certainly realized it when he sobered up and/or calmed down.
The second reaction you got when saying - ok, I won't contact you again - is just more of the same out-of-his-senses reaction you got from the first text. Even if you assume he never understood what happened, there is no reason for that kind of reaction.
It's hard to leave it like that, I know, it would be great if it had all been kind and civil, but that's not him.