You were right the first time. Climbing is a largely constrained problem solving exercise with binary outcomes (you either did the route or didn't) and a built-in level-up style progression in the grading system. (Today I did my fist V2! etc...) You can do it entirely on your own, at your own time, in your own pace and it's not really possible to "lose" at climbing[1], you get unlimited attempts to try and figure it out. You can, for outdoor climbs, try the climb, fail, train for 6 months and retry the climb to succeed. In short it's almost designed to be addictive to coder types, but all that came before the indoor walls, not after.

Source: I climb obsessively. They got me good.

[1] - competition climbing aside, obviously

You can add free soloing to the list as well.