This is the email I got today.
Dear *******,
Your video may have content that is owned or licensed by WMG.
No action is required on your part; however, if you are interested in learning how this affects your video, please visit the Content ID Matches,
Same thing happened to me a few months ago. 
ya me too 2 videos muted…lol
This does 
They’re being so “legit” lately that videos that don’t even have sensitive content on are being muted…
It happened to one of my videos stating “Your video has copyrighted content from ******* and has been muted”
the amusing thing is, my video didn’t have any audio at all 
I muted the audio stream 