Even with family and closest of friends, we have no idea what their situations are.
He may really have needed the money, I would not judge. I would have been thrilled to give him the money and moved on.. He did you a huge favor. It was last minute and it was your responsibility to figure out how to take care of it. You were going to pay someone anyway, why not your brother?
Maybe next time "trading" with your brother.. "I will take one of your weeks this next year if you will do this for me. "
I think you are just really stressed and because you would have just mowed his week for no cost, do not assume everybody is like you..
I have offered money to my sister for doing favors for me.. ( I know she has financial needs) and to "save face" for her, told her to "use it on the kids"..
I do not want her to feel "proud" around me, but I know she really need the money .