I'm not any expert. But from my experience, I would replace the string ever 2 years if not every year. I have a older Jennings compound bow that I had a zebra string put on it about 5 years ago. The bow is only used for bow fishing a couple times a year. The bow is sitting upstairs on my bow rack with a broken string. Broke about half way around the top cam. My guess is your string probably had enough dry rot andit broke. I don't think its from twisting your cables to the lower cam. I'm no expert though.

Chief