Maybe an injury during capture? I had a kuhli loach that had a more pronounced "kink" that gradually got much less notable. It seemed to live a normal lifespan while I had it, ~8 years (rehomed to move).
There are some diseases & old age that can cause spine deformities sometimes. But from what I've seen (on shorter bodied fish), it's more close to the dorsal fin area.
Does it eat well & seem healthy otherwise? If so, I wouldn't be overly worried.