Q: Why is does it say that my Iphone is a replacement

I purchased a used Iphone for my girlfriend last christmas. I met the guy at his house he was around 50 yrs old look very legit with his kids and everything. He told me that he had it for one year and wanted the 6S plus and that he bought the Apple Care Plus, which I verified (there was a year left of warranty on it). But, yesterday, I checked back just to remember the exact date and now it says that my Iphone is a replacement and that I should contact Apple. The problem is that when I bought it from the guy, we went (both of us, togheter) to the Apple store in Laval, Qc, and ask the employe if I could transfer the ownership of the warranty and he had no idea what I was talking about so he told me to call Apple. We did, togheter, called Apple directly in the Apple store. The girl at the Apple support told me that we didnt need to transfer the Apple Care Plus warranty because it is linked to the phone serial number, and not the owner of the phone. She said that she had never done that before and it was unusual that someone ask to transfer the ownership, but we talked to her for about an hour to finally hear that her system wasn't working well this day so she couldn't made it. She said that she would get a note on the profile and make it when it becomes available. I really don't understand now why I have this message it feels like the guy that sell me the phone called a replacement but never send it back cause he sold me that replacement but how is that even possible??? I mean I have is name/adress I could report him it's like a fraud to do things like that!!