How do I know? Because I’ve never seen a single study that concludes minoxidil causes sexual side effects in a placebo controlled study. I know you will say (again) that there is more to all this than placebo controlled studies, but there really isn't.
You put forth an interesting hypothesis: "minoxidil is a blood pressure medication. Blood flow/circulation is obviously linked with erections"
That's great, it's one of the first steps in the scientific method. However, my big problem is that people skip out the important steps (running a test, analyzing data, etc) and just draw a conclusion based on their hypothesis. That is junk science. It may make perfect sense, but it isn't fact until it's been tested. It shouldn't even be used as an argument until it's been tested.
We can all sit here and say there's always chance this caused that, so let’s focus on this being the cause, even though we have no science to back it up with. In Timi's unfortunate case, he is blaming minoxidil. We could say "well you never know, there's a chance it caused sexual problems, so that's probably what caused it. After all, nothing else could possibly cause sexual problems in a young man"