High Blood pressure is mostly asymptomatic which is why it is so dangerous. They've tried to link high blood pressure to headaches and it has not been definitively linked thus far. Although I think many with hypertension report they get headaches. Bad headaches should be investigated though as it could indicate blood pressure is exceptionally high. When pregnant and I had pregnancy hypertension, that was one of the warning signs of eclampsia they told me to be on the look out for. This article is helpful I think. The American Heart Association has taken a stance that headaches are not correlated directly to HBP unless it is extremely elevated. But I'd tell his doctor anyway to discuss. https://www.medicalnewstoday.com/articles/322451.php#what-does-the-science-say
I had a coworker who complained of headaches. I urged her to go to the nurse down the hall to check her blood pressure, during a headache. She declined. She was stupidly frugal when it came to health care and medications. She died as a result of the stroke that struck while getting ready for work one morning.
I also have high blood pressure. The headaches were early morning waking me up. My lower number was 110 during the appointment. I started medication and sleep became normal again.