How iPhone connect to 3 HFP devices simultaneously

I am test engineer in Bluetooth HFP profile, and I am bit surprised when I checked that my iPhone (iOS 11 and 12) can connect with 3 HFP devices at a time.

I can connect my iPhone with three Bluetooth infotainment system, after that whenever I am initiating an incoming call all three HFP infotainment system rings, whenever accept a call in 1 HFP infotainment system then other 2 HFP infotainment system goes to privacy and we can switch from privacy to active according to user's need but at a time only one infotainment capable to route call audio. I have seen this earlier if face time is turned ON but here I turned it OFF and still problem is same, I read that there is dual audio concept in iPhone but that is related to music not with HFP I am not able to understand how could it be possible that one iPhone connect for 3 HFP at a time.

Please suggest it is a bug or new technology added in iPhone's Bluetooth.

Thanks in advance!