My son's are almost 3 and petrified of shower curtains. They get a little claustrophobic. Plus they hate flushing the toilet, because it makes a huge noise.
I just take my shower curtain down. Lay a towel infront of the shower, because it does leak a little.
As for the pooping in the bath, accidents happen. He is in a new environment, and may be a little nervous. Don't worry about it. He is still learning.
As for the whole naked thing. Some people aren't comfortable being naked. Some people don't like their children naked, and have taught them it's rude.
I would say No to the abuse, I am thinking it's his parents being uncomfortable with him naked around people.