Tilt or not to Tilt

So in my last ranked match Kayne was afk for 3 minutes and came back as I was typing /remake and I thought to myself maybe he can catch up. At around the ten minute mark he comes into bot(My lane) and sits in a bush in the lane or maybe a minute then suddenly flash's and uses his ability on nothing then chases a half health Jhin and full health support under tower and dies. It was literal inting and then when I asked why he did that he said lag and I totally tilted because he was behind from an afk and fed jhin. I asked the other team to report him because I believe flashing and using ability on nothing is not lag. Then my whole team started flaming me and saying they were gonna report me since you can't report someone for lag. Was I justified in tilting? I didn't flame him a ton and the game ended with the Riven and him the Kayne flaming the hell out of me and I was so pissed. Like this guy was 3 ranks above me and I feel like he was inting. Should I of just ignored it and went on with the game?