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Sadly, your friend left something resting on the keyboard so when he closed the lid it pressed on the screen damaging it. The back glass which is where the metal oxide is etched onto is a bit more brittle than the cover glass side. The physics of the glass shifting a minuscule amount can cause it to crack the back glass not the front glass! Here’s another person who just encountered the same problem How do I fix colored lines down my screen caused by pressure? Here’s the needed part: 13” MacBook Pro Display Assembly - Space Grey, Apple P/N 661-0797013” MacBook Pro Display Assembly - Silver, Apple P/N 661-07971 And the guide to put it in: MacBook Pro 13" Function Keys 2017 Display Assembly Replacement
