Sorry to take so long to get back to you lovely, fish can have odd moments, but usually there's a reason for it. For example one day on a Friday my goldfish bottom sat so I coaxed her with a bit of food and she was fine, a few days later when doing my water change, I realised the filter had been switched off for an entire week (I had evidently forgotten to turn it back on when doing my last water change) and so ya see the reason for her bottom sitting was more than likely because the filter had been off for 5 days.
So I suppose what I'm trying to say is that fish can act odd for a number reasons, so I would just keep an eye on the little one. If any of the fish seem to bully him again (sometimes fish do pick on weak or sick fish) then seperate the fish
As for tank decorations, fish don't need it, but at the same time it's nice for them to have something there, ya know? I personally only have mopani driftwood and gravel bags (gravel in some tights) in my tank, algae grows on it so Lucky nibbles at it constantly.
If you think the decoration could cause injury or problems to the fish, then simply if in doubt, take it out
Have you been able to get any photos?