I've owned about 5 Dumerils and I have yet to see them strike once in hand so I would that he was still in feeding mode.

Most of my Dums have struck at the glass and anything I put in the cage, but don't even flinch once out. It's a feeding response and you definitely picked him up too early. My current Dums feeding response can last 24hrs. T

They are ambush predators and seem always to be ready to spring into action when in their enclosure. They are also sloppy strikers. Only snakes I've owned to routinely get a mouthful of Aspen and even bite themselves. There are no plastic tubs or newspaper in the wild so I wouldn't worry too much about them swallowing substrate.