How does Reliance Standard classify a stroke?

My husband suffered from a stroke in 2011. He received STD and LTD. In our policy, it had stated if he had an injury, he would be covered for 5 years and if he had an illness, he would be covered until he was 65. He was 49 years old at the time of the stroke and that’s a difference between 5 years and 16 years. It’s been 4 years now and we received a letter stating that he is considered to be totally disabled and will continue benefits until 2016. My major question is, is stroke considered an injury or an illness?