It all stems from fatphobia and basically blaming overweight people for being overweight when it is widely recognised obesity is a disease and guess what we now have medical help.
Why should it bother anyone what medication another is on regardless of what it is for?
You could always ask for a couple of haynets worth of their hay and mix it in with yours for a couple of days. The small bagged haylage could be a lot stronger than the one the horse has now
Yep leave them they will eventually decompress and you will be their source of food if nothing else and they will be happy to see you. But you may never have a lap cat 🐱
Is there a Facebook group where you could ask? If it allows you to ask anonymously even better as then no one in the unhelpful riding school can say anything about it