Another musician here:
One day I got ads for Waves Plugins. I still haven't figured out how they have learnt about me being into producing. My FB friends are (afaik) non-musicians from school days and I don't open FB in my regular browser. Furthermore, I block almost anything µblock has to offer in my normal browser. Maybe they derived something from my e-mail address. Pretty scary stuff!
I don't think it's impossible for them to see your financial (Credit Card?) records and use that too? Advertising companies are after all, advertising companies... They get anything they can, even the old way of finding things out. I used to buy cigars online, to this day I still get mail from websites / companies I never bought cigars from.
