Leaverbuster Timer

I don't understand my recent leaverbuster. I just got a 20 min leaver buster. I was afk, because my net was being crap for the first time in a while, for about 7 minutes in a ranked game bronze 2. I haven't afk'ed for over a year now, but it isnt 5/10 minutes. W h y. I play every single weekend and havent afked for ages. Why?