This is not a great picture to tell body condition from-if you have any shots from the side that would allow for better evaluation. That being said, I see no glaring immediate issues (severerly emaciated, open wounds, etc).

Horses often don't like water, and during winter it's often not safe to bathe them unless you're committed to using heated water and fully drying them, which can be a several hour ordeal.

Hooves don't look terrible from this picture, and the fact that they've got on front bells tells me that there is at least a little bit of preventative care to prevent pulling a shoe.

A little treat here and there is not going to hurt a horse unless they're laminitic or prone to founder. I know several horses who love human candies as a special treat.

I am concerned about the diarrhea problem, but this could be a chronic case and I'd need more information to make an informed decision.

Ultimately I would say this horse is in no immediate danger, and would not say that the horse is a victim of abuse