Thai massage caused back to crack, is that good or bad?

Identify problem. It is not likely addressing the underlying problem.Most cases I see are due to sitters disease or gait (ex; foot position). But you need to identify the origin and rule out more serious causes. Any neurologic issues like numbness in the legs, no muscle weakness, no fever, no urinary pain, fever, genital discharge, acute trauma, insect bites, etc https://www.youtube.com/watch?v=8TO8Il3vdxQ.
Neither . As long as the crack was not painful, it was not "bad." having your back cracked routinely can make you feel like you need to have it done all the time- so not necessarily a great thing.