I've made a few extensive posts about this here before too. Had 24/7 RSI paint for years. At the worst I couldn't hold a mouse.
Thousands of dollars of ergonomic chairs, keyboards, and so on made it so I could work but still had constant pain.
Started doing pushups (which I had avoided because I thought they made it worse.) Four weeks later I was using a laptop and suddenly it hit me I had been typing for 30 minutes with no pain. Life changing. Zero pain now and I can work 12 hours straight.
Definitely is some combination of the muscles and tendons tightening up in the arms and shoulders. The pain being in a different spot makes in misleading.