I'd have done exactly the same as you. I once used to give a lad a lift to school with my boys and one Monday his Mum phoned me and said he wouldn't be in school that day as it was his birthday and he wanted to spend his birthday money. I couldn't believe it, especially as school was breaking up that Wednesday for 2 and a half weeks, and I knew that they were going to Disneyland Paris on the Friday for a long weekend. I think I would have told him to save his money for then. Not only could I not believe that his Mum was pandering to him so much but it put me in an awkward position as the teachers were asking me where he was (I just said that his Mum had phoned me and said he wouldn't be in).
I think that by keeping children off school just because it's hot sends out the wrong message totally, they have to learn about commitment, whether to school, work, people or whatever, and how better to learn that by parents setting an example.