I'm guessing you mean trademark, not copyright -- copyright does not make sense in the context used -- but I'm not sure why you think it would be trademark infringement.
if they want to keep it, they should come up with a viable long term business model, because obsoleting hardware isn't it. otherwise their threat hopefully will vaporize eventually, along with their non-ip stranglehold.
perhaps they meant something like “hmm, couldnt streaming copyrighted music using this app constitute a violation of rightsholders' intellectual property?”, which, on the one hand: haha; on the other hand: lmao
I was about to write a comment about how I'm not supporting a company that ruined by Google Home speaker group functionality so yeah I think Sonos would have a pretty good trademark infringement case here.