I’m surprised at that. I never got the cane at school at all, but I knew one boy who went to a different school and was caned both ways. I remember him saying that two strokes on the hand were agonizingly painful and left his hand swollen, whereas he found that two or three strokes across the bum (presumably over his normal clothing) stung for a couple of minutes but then started to wear off.
Some older teachers were ‘softies’, and probably were losing their muscular strength anyway.
You really don’t need great muscular strength to deliver an effective cane stroke. It’s all a matter of timing, including a nice snap of the wrist at the last moment