no glue on new screen why?

when trying to replace the battery on my galaxy tab E t560 I watched a video on utube which showed removing the screen first and the back would come off at the same time. I tried this and managed to cut through the cable for the screen. At this point I wrapped it up and sent it to the repairer I also sent him the new screen. However he phoned to tell me it was not a genuine screen and did not have any glue around the perifery so I am at a loss should the screen have glue( its more like a mastik) than glue. can someone give me a clue to go next.