FWIW CMG doesn't claim that this is from smartphones, and instead ambiguously refers to smart home devices (and I would be shocked if say, Google allowed a third party to access its microphones for Google Home devices). Similarly, there is no way that the FB app is doing this (for one thing, you'd see the microphone icon on your OS) — the "FB partner" here just means FB buys some rolled-up marketing info from them, probably with zero idea where the data comes from.

If I had to guess, I'd bet this is from shady smart TV manufacturers, who have a long history of spying on their users and selling that data.