Maybe the stop/start system knew the battery was on its way out so decided not to risk it. A shame it didn't think to let you know a new battery would be needed soon. 🤔
Yes, moderns and their electronics. Recently mine had a failure in one of the ABS sensors on the wheels, this resulted in the dash lighting up like a Xmas tree with upto 6 lights, sometimes it reduced the number once moving. It also disabled the stop/start function (which rarely activates in daily use due to driving/road conditions) and the cruise control, which I hardly ever use but did want to during the period between identifiying the fault and getting it repaired.
When it was repaired it took me a day or two to get used to not having all those pretty lights on - I sort of missed the excitment of which would come on and which would stay on.