Ignore him. He's subtly trying to control the situation behind the facade of sounding semi-reasonable whilst at the same time putting you on notice that he doesn't want you in her life.
I recently had a friends ex call me at 3 in the morning spouting rhetoric (he's gonna knock my head off, don't email or text her, it won't be pretty, etc.). I did not engage him at all and I accomplished 2 things;
1. I took the high road, so I scored points with woman.
2. It drove him nuts that all he got from me was a chuckle and a dial tone. his reaction was a real turn off for her (not that she was considering a reunion with him, but it made him look worse in her eyes and made her choice seem even wiser).
Let it slide, be the adult. He'll bury himself soon enough.