Cracked screen turned into broken LCD?

Last week I cracked my screen. Took it in to be replaced and the guy said it was just the glass cover that needs replacing. So he replaces it and puts it under the light and I come to fetch it and everything looks great. 10 minutes after I leave the store I notice a small little light spot in the corner of the screen. But as time passes, the light spot just gets bigger and bigger. The next day I took it back and he tells me the glass is lifting and he needs to put it under the light again and I should pick it up the next day. So next day I go fetch my phone and he says sorry I need a whole new LCD. I asked him why we couldnt just replace the glass again and he said that the glass wasn’t the problem. The LCD was. My confusion comes in with this. Why is the LCD now needing to be replaced when there was nothing wrong with it to begin with? Did the glue destroy the LCD?