They get active when they're hungry and looking for more food. If he's eating well, then it's normal LOL.
If he's roaming during the day as well though, he may be too hungry or something is stressing him out.
If you experience almost any snakes outside of ball pythons, ball pythons are indeed relatively shy and more sedentary. They're also totally nocturnal, so owners tend to not see their activity since it happens overnight.
Compared to carpet pythons, all colubrids, other semi-arboreal species, and nearly every other snake species- yes they are actually a lot more inactive. Handling a ball python is also very easy and slow-paced- often they will just sit around. That's why people describe them that way. lol