What was confusing was chain length. So I played with that option. Your IK bone is not counted and there’s a few bones to the leg. Chain length 1 is the shin (0) plus the foot. 0+1. Chain length 2 is the shin (0) , foot (1), thigh (1) .
0 + 1 + 1 = 2.
You also don’t need to know this for this segment or model but maybe for the hair portion or a mesh that had multiple segments. Those simple parts inside menus always seem to make weird results later.