Suspension at the slightest whiff of afk-ing (LoL)

Idk whats wrong with this game I played the game from beginning to end and didnt stop once and they just slapped me with a 3-day suspension for "inactivity". I really don't think I stopped playing once maybe the game took like a minute to load at the very beginning? But thats literally it and nobody complained.

Also since when do u get banned for being "AFK" ? What happened to LP penalties and low priority queue?