At a guess, I’d say 90+% of horses I have met were pretty rude or pretty stressed when offered treats. Yet, we take it for granted that all our horses are relaxed and polite to be hand treated.
I think the point I’m trying to make is that even though we talk about rewarding a horse for its effort, as an essential element of the training process the concept is entirely foreign to horses. How much this affects how we apply a reward will depend on how much emotion we attach to the term.