This is a beat repeated topic LOL.
There have been studies finding wild adult male ball pythons in trees for hunting purposes, and finding their diet consists of birds, so they do obviously climb. But they climb for hunting reasons. Adult females climb even less, and are rarely found in trees. Just because they can climb, it doesn't make them "semi-arboreal" which is a classification.
My dumeril's boas used to climb on her branch when hungry and hunting when she was younger and smaller, as they do. Does that make such a terrestrial snake as a dumeril's "semi-arboreal"? Absolutely not! When they get older and larger, they become strictly ground dwelling and never climb. So I took that branch out when she totally stopped using it LOL.
That being said, since balls CAN climb when out hunting, many people provide them with climbing opportunity to do so if they want to, for enrichment purpose.
Ball pythons in captivity have more possible reasons for climbing though, especially in beginner keepers, because husbandry and setup is a factor. They also climb when stressed, trying to search for a more ideal temperature or spot.
I'd say for your case, he's most likely cold and trying hard to look for ideal temperature.