When a bow is "high strung" it means that when the bow is strung the height of the string from the handle is over 6 inches. This made the bow fast to shoot but over-stressed the wood causing the bow to have a very short life. When a bow fails it tends to explode.
So a "high strung" person is quick to blow up. Quick to anger, etc
The high strung mall security guard told me he'd kick my ass if I tried to skateboard again.