AFK for 4 minutes

I wanna know why i leave the game for 4 minutes, because the light of my house just turn off for a sec , so i have to turn on the computer and all that stuff, and i don't recieve the points of the game, they just quit me points, i was vayne, i was carrying my team, literaly i was the best score helping my team we were so good, they start to lose when i leave the game, then i came back and we won, like it was a 38 minutes game, i just left 4 because the energy, i play so good, i didn't feed and i had no bad score 6/3. Tell me that i left 10 minutes or that i feed, or that i didn't came back, like just don't give me points but don't make me lose it. Thanks! it's unfair.