What he's done is a few things.
Petstores are NOT known for being able to properly handle these species, employees don't have the time to wait patiently for a cham to get out of the cage.
So it's experiences with the big hairless apes isn't the best.
Depending on his age, he's matured into an adult and as an adult "personal territory matters" where as before if they're young, it's not a huge issue. But for males and some females it really does and so they'll put on a display... as long as they're inside that space.
Once out, there's nothing to defend and a resulting attitude change.
Bigger habitats are not better.. size really doesn't equate to improved husbandry past a certain line... it becomes a negative. I know that there's a pod caster that pushes them... but that's because he sells these oversized cages in his own store and makes a lot of money off of each one.
The 2x2x4 means that it can run away from you and that causes panic and more stress and socialization issues. IF they know they got nowhere to run, then there's less of a issue and with proper handling techniques, far less stress and problems.
a 18x18" screen cage is perfect.