some hypertension is caused by other diseases but not all the time. Pearl's cardiologist spent 7 yrs looking for the cause of her not-quite-under-control hypertension. But in the end, it was idiopathic.
I did mention this to Dr. Couto at one time and he said that greyhounds do seem to have idiopathic hypertension.
But do keep an eye on it. I thought we were doing very well when one day during a walk Pearl's eyes were moving rapidly and she was swaggering. Lasted maybe 30 seconds. I thought vestibular, but decided to check with her cardiologist. Vet said come in now. Pearl's BP was 300. From that point on we did a BP check every 6 weeks.
However, in the end, I lost her to cancer.