Why is an android user mms messages coming in to my iPhone X ina separate chat?

I just upgraded my phone from 6 to iPhone X today and my friends messages are coming through normally but when he sends pictures they are in a separate chat between his phone number and mine. It shows up as a group chat not a regular text. He has an android phone and I didn’t have this problem before upgrading... I checked his contact info and he is under “phone” not “iPhone”