Devices with different Apple IDs responding to the same FaceTime calls
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.