I think she may have oversimplified it. While headaches CAN be caused by blood pressure, your readings never get high enough for that to be the cause, which is why you’ve been told it isn’t your blood pressure. Your numbers are very well controlled, and if high BP were responsible, it would clearly show up in your readings, which it doesn’t. This doesn’t mean your blood pressure is elevated nonstop.
Well controlled blood pressure, like yours, does not cause chronic tension headaches. Headaches that last for weeks aren’t a sign of sustained high BP, especially when readings are normal. If anything, it may have been a brief spike that came back down quickly, and that doesn’t cause long term harm.
You don’t have weeks long high blood pressure. What you’re experiencing fits tension headaches, made worse by stress, muscle tension, and TMJ, not dangerous hypertension, especially since your BP readings are fairly normal.

Your NP is very knowledgeable and you should definitely listen to her, but it’s also worth remembering that medical explanations are sometimes simplified. The propranolol should help a lot.
It sounds like you otherwise had a good appointment, especially considering how stressed you were beforehand.