Comment by Twey

Precise causes of RSI are, as far as I know, still largely unknown, but (at least as far as current hypotheses go) there does have to be some kind of strain involved.

From a quick search, it seems piano players do suffer from a high incidence of RSI (e.g. https://pubmed.ncbi.nlm.nih.gov/12611474/, which also correlates it with smaller hands, i.e. more stretching).