My mom has had very high blood pressure for a long time. She was going through a period of being off of meds and had been for awhile. She decided to smoke one night, well, a few different nights. each time she smoked, it lowered her blood pressure, but to normal levels.
So weed itself can lower blood pressure which is why it shot down so low. Weed wont lower everyones, though. It will still depend on the person and how they react to it, and it depends on the weed
Happy toking