[quote=@Guilty Spark]
He hit the platform so hard their individual chains broke?
[/quote]

He's that boss.

More realistically speaking, the situation might be where they weren't individually chained at the feet, but had one chain runner between all of them (or per 5 or 10 or whatnot), that was attached to the platform. If the platform breaks, everyone can free themselves from the runner pretty quickly.