It might not be trivial to achieve technically, but at the point you have multiple speakers dotted around a multi-room space, making them all play the same thing in sync is a fairly obvious idea, which I think is more what is being argued here.
Depends how broadly it’s claimed. A detailed claim that gets into the technical specifics of how this is implemented might well be nonobvious. A broad claim that covers all possible ways of synchronizing audio is a tougher sell.
But the patents are often not on the technical implementation nitty-gritty, but on the very general idea of "Two speakers that play the same song in sync".
The latter ("concept patents") just stifle innovation.