Over 30 years ago, as part of a new job, I had to go for a medical screening. For the first time in my life, they said I had borderline high blood pressure. They had me lay down, turned out the lights, and 5 minutes later, they took it again, and it was low. They made me come back several days in a row, repeated the procedure, and announced that I had "white coat hypertension."
I read it myself at home with some regularity for many years, and it was in the normal range 99% of the time.
I've never taken anything for it, nor have I modified my lifestyle, which some would describe as sedimentary with improper diet.
Today, I'm over my white coat hypertension, and even at the Doctor's office, I don't have BP issues as a rule, except maybe when seeking treatment for an acute injury or sudden illness.
I would say "Leave the guy alone." Don't make a big deal out of this. Let him check his BP himself on his own schedule, when he feels in control, and comfortable. It may not be worth treating.