>I personally have my doubts whether it has to do with blood pressure

If you're referring to scintillating scotoma/visual migraine aura, it's thought to be the result of what's called a cortical spreading depression: https://en.wikipedia.org/wiki/Cortical_spreading_depression

It's really fascinating stuff (and pretty unnerving, speaking as someone who experiences migraines with aura).

On the blood pressure connection, propranolol (a beta blocker often used to treat high blood pressure and anxiety) is often prescribed as a prophylactic for migraines, but I'm unsure of the preventative mechanism(s) at play.