> There were product managers on both sides of that decision to prioritize enabling such a stupid feature.

Probably not. And that is why it happened - nobody thought about this at all until everything working as designed fails.

That is the thermostat probably is an off the shelf tablet with a speaker that they put other things on to make it a thermostat - this is the obvious thing to do and a lot cheaper than making your own completely custom hardware for this job. The software on the thermostat is likewise off the shelf (probably android) which has spotify in the base install and nobody took it out. Then you set the thermostat to be in the living room - again because that is the obvious thing to do. Finally your wife plays music and spotify sees two devices in the living room and picks one - which happens to be the wrong one but they have no way to know that.

The above is entirely likely and at no point (until know when I point it out) has anybody thought of it.