I almost feel like hiding would be something hatchlings do more than adults. While by nature they are cautious, these animals have never seen a predator in their life, and if handled well, dont have any reason to fear the handler. He may have just realized that nothing bad is going to happen to him haha.(None of this is scientifically backed as far as I know. Just my theory) If snakes are capable of medium-complex association I cant see why they wouldnt explore more as they get older and more experienced
Edit: I just watched the video. That looks like a bit of a small enclosure to me. What size tub is it? At least from the video it doesnt look long enough to provide a good heat gradient.