Most plecos unless quite large,,will often be on the receiving end of such harrassment as you have witnessed in a tank of cichlids. Is why I would opt for a larger species such as the Synodontis I mentioned some time back when you expressed interest in something suitable for a cichlid tank.
Cichlids may have inflicted internal damage to the pleco and this could be affecting it's ability to navigate. Seems possible that fish may also be adjusting to possible difference in water parameters from dealer's tank to yours considering you opted not to quarantine, and the fish has been in the tank for lesss than 48 hours. Fish could also be sick.
As your signature indicates,,I would want to be more aware of possible issues with fish than the LFS.
If it is a large waste producer like the Common Pleco
that intersts you,, I would look for a larger specimen that may be better able to defend itself in your tank. Until then.. I would keep a close eye on behaivors of the fish and be prepared to rehome the juvenile pleco if this appears warranted.