I've also never heard about the rule that children cannot be left unsupervised at nap time but rules are set at a provincial level and vary. I'm not sure where you are so it's harder to look and check to see if you are applying rules from a different province to your situation.

At two, he's young. Some children do chatter more than others even when settling at nap time. It's just his personality. I would ensure he's getting lots of outside time, all year around because if he's tired, that will be a big help in reducing the time. I'd also move him back to where you had him isolated (where you can still see all children) but remove any toys or activities from his crib/play pen.