I'm an ectomorph small framed guy,, 5'10 185 with a 29 inch waist.. So not huge arms,, cuff was probably fine.. It was like 170/95 on my home monitor,, and even higher when I went to the doc..
Before I left the doc office they had me lay down and relax and rest for 20 mins or so,, it came down and then they let me go home, but was still high.
Personally, don't know if there is any medical evidence for this,, but I think significant muscle and weight gains itself increases blood pressure as well especially when it happens quickly.
My going from being sedative and recovering from back surgery (having lost a lot of weight),, to putting on 22 lbs quickly may have played a role in the elevated BP