Basically i suggest showing some basic knowledge about this game in the game but not just on website, including what called 'afk'.

I player an AI game just few minutes ago. This is a new account so my level is low.
Unfortunately, my network begins to have problems, lagged so badly an i almost could do nothing.
So i reconnected and still not work. Then an restart my computer. Then finally works.

Then i come back to game, i was told i had been reported 'afk'.
Then i tried to explain to them i did not disconnect on purpose, my network was so bad that i had no chose.
Then they just argued that stay in base for 15 min is 'afk'.
And i told them to search what 'afk' actually means before report.
They said 'afk' means not active.

Ok, that is what i encountered.
I just want to say, if my network is ok but i just do not want to play, that is 'afk'; if my network is so bad that i cannot play, and i continue to try to fix it, that is not 'afk', or at least should not be reported. (Or you can help me report my network server.)

Certainly all those high level players know this, but not those beginners. And i do not think beginners know to search online about some basic things.
That's why i suggest to post this basic knowledge in the game.

While afk is an acronym for away from keyboard, the actual report reason is for "AFK/Leaving"
Staying in base for 15 minutes is a suitable reason for reporting as you've definately had a negative impact on that game.
One report isn't going to result in punishment, but might i suggest you not play if your internet isn't reliable? get a hard-wired connection to your router, ***** at your ISP, whatever it takes, but if you repeatedly stay at base for 5+ minutes, even if it is due to network reasons, you are going to get banned.

you do not understand
it's nothing about punish or not.
for example, if i am lag so bad, i have two choice: 1.continue to play while lagging and feed enemy; 2.try to fix it as quickly as possible.
if i choose 2, my team is 4v5 for 15 min; if i choose 1, my team is 4v6 (i will lag in vital moment, and that will be a feeding) for whole game.
which has more negative impact?

i do not care about punishment.
just say that this is wrong.
And you say AFK means away from KEYBOARD.
while i am fixing my network, i am still on my keyboard but just quit the game for some time.
is it logical?

People report falsely more often than should happen. People get reported for feeding even if it wasn't intentional (unintentional feeding is not a reportable offense, so those who report for it often soon see their reports become worthless), and the same goes across the board pretty much. The tribunal (should you ever get there) seems to be generally capable of distinguishing between legitimate and false reports, and if you find youself in a situation where you think you were unjustly punished, you still have recourse with Riot. In short, I wouldn't worry too much about it, but if you really are having ISP trouble, you probably want to fix that anyway.