Don't feel bad at all for doing this. Good Job! More & more people are speaking up now for poor judgement, not only for animals, but also for children. There's no excuse for not knowing the dangers as so many sad, sad stories have been told and televised.
We were in the grocery store the other day on one of those HOT days. They announced on the intercom that a specific car had a dog left inside & were calling the owners!

Someone had reported to mngmt & rightly so!