To get back to the OP's post, I'd like to think that the cleaner was checking the toilet paper/soap levels, or doing his job, but if he had no cleaning equip with him, then...sounds like he was actually using the loo. And those rooms usually have only one loo, so does it really take 5mins to check the paper and soap levels, or was he the one taking the big stinky poo? If he was doing his job properly and not using the loo, then surely he would have returned in a timely manner and cleaned up the poop?
I, personally, would email the centre. At least then they can discretely remind all staff to use the staff loos (and of course, one can mention one was not sure who made the mess), and can try to ensure messes like that are cleaned up quickly.
I try to only use parents' rooms in busy centres. The one at our tiny shopping centre has such a low ceiling you feel claustrophobic in it. And staff come and go to microwave their food...hardly space in there for a pram, either.