AFK in the context of a bg doesn't just mean away from keyboard. If you go in a bg just to fish or fight rams, then you are AFK and should be kicked.
"This does not mean that 2 minutes without being in combat is being AFK" ... true in some cases (like when you go straight for the last bunkers / towers) but in a lot of cases, it does mean afk. As i said above, if you go fishing in bgs, you are afk. If you just stay in stealth the whole game and watch other people fight, you are afk. If you stay in stealth, get reported and then you attack just to enter combat then you go back in stealth to do nothing, you are avoiding afk kick. There are a lot of examples.
"Try going into combat within 2 minutes when you spawn at one side of the map and on the other side"... if you got killed while you had IDLE, that means you were afk for some time and if you don't reach the fighting place in time, you do deserve to be kicked.
Apparently it is you who doesn't know what afk means in the context of a bg.