IPhone – Stop iPhone from ringing on the Mac in Mojave

Yes - this technology seems to be driven by your contact card info stored by calling party. If calling party has info for you and someone else in same contact card, then both phones will ring for FaceTime even if not same Apple ID.

In our case, we had friend who had stored my number and husband's number (not email) under my contact card. Both our phones would ring when friend tried to FaceTime me, even though husband and I have separate Apple IDs and caller never selected the other number.

Solved it by having calling friend remove the additional phone number from my contact card on his machine.

Easy Peasy.

System Preferences > Notifications > FaceTime > uncheck 'Play sound for notifications'

Alternatively, you could just turn on 'Do Not Disturb' from the Today/Notifications widget easily when you need it by clicking on the notifications button in the menu bar and scrolling up the 'Do Not Disturb' setting will scroll into view