In my real world career, part of my job was to coordinate research project meetings and conference calls with teams of MDs and PhDs, sometimes quite large (40+) groups ... I know that if I failed to issue appropriate reminders, attendance was always low.
Well, is that really analogous? Not to defend the OP's unnecessary aggravation over this non-slight, but... these meetings you arranged and reminded these "mature adults" of, were they previously scheduled standing weekly events? Or were they one-offs or randomly-occurring events that required custom scheduling?
One-off or random events, yeah, a reminder is a good idea. But something I do the same time, same day, every week? That everyone agreed to? That was already confirmed less than a week ago? Reminder shouldn't be necessary AT ALL.
In the OP it was clearly stated that the recurring rehearsal day has been previously discussed and agreed upon as a standing weekly event, and confirmed again after each rehearsal. I don't defend him being perturbed by a simple confirmation text, but at the same time if it were me I'd def do an eye roll when I saw it.
If someone has a problem crop up where they can't make the agreed-upon standing weekly rehearsal, THAT'S when a message is needed, and the earlier the better.
Band I'm in now, we don't even touch base regarding gigs... we show up when we're supposed to. It should be on your calendar, you should not need a reminder. And we don't. We're big boys, we know how to act responsibly. But, previous band, the de facto "leader" would send a reminder the day before or morning of. No big deal, I would send back a thumbs up or just mental-note and move on.