It depends what size engines they were using, and the rocket. Payload affects height dramatically too. If you're going to shoot payloads, you gotta have a good sized engine and know trajectory, wind direction, etc.

These guys probably tried to stuff a Walmart Estes rocket with their stash. In that case, I bet it would hardly reach 100 feet being shot from a moving car all loaded down like that. Funny scenario would be if it barely launched out of the trunk, and just crashed into the highway a few feet behind them for the police to pick up, haha.