Quite possibly the guy was suffering from a mental problem if the usual culprit, alcohol, was not a factor.
It sounds to me like it was handled well from a security point of view, he was put under control before the situation escalated and he wasn't killed or injured. There have been fatalities in recent years in similar situations.
As far as using duct tape, perhaps the hand restraints were not easily accessable from the cabin. Or maybe the air marshal was one of my neighbors...