Tendinopathy is a type of tendon disorder:
Traditionally, tendons have been considered to be a mechanism by which muscles connect to bone as well as muscles itself, functioning to transmit forces. This connection allows tendons to passively modulate forces during locomotion, providing additional stability with no active work.
The difference between non-insertional and insertional is that the insertional tendon is where the tendon meets the bone and non-insertional is the 'in-between'. And so the related injuries are different - insertional tendons can come loose from the bone (e.g. tearing), whereas non-insertional tendons can't.
I think this is what the author is implying (that non-insertional tendon's have less possible forms of being injured, and the main one is caused by repetitive stressings).
Tendon injuries are covered here:
Tendinopathies may be caused by several intrinsic factors including age, body weight, and nutrition. The extrinsic factors are often related to sports and include excessive forces or loading, poor training techniques, and environmental conditions.
which is from the reference given: