PvP non-participation basically means that you were found to not be participating in several Battleground matches. If reported by others in the Battleground as afk you will usually be given a temporary debuff that requires you to get into combat within a short duration. If you do not get into combat you are removed from the match.
It is important to understand that not being removed doesn’t mean nothing will happen. We have systems in place that collect data over time and those reports and that data are used to verify non-participation.
That you may participate in some matches does not negate those that you may not be participating in. I’m not saying specifically “you”, it is just an example as I have seen some that may not participate in one out of four matches. They do great in three, but are otherwise not active in the one, which is still non-participation.
Game Masters are not able to discuss with you the whys and wherefores. They review the original action and verify if the evidence supports that an error was made, that you were compromised at the time, etc…
If you feel an error was made you may appeal, the case will be reviewed, but again, our staff will not be able to discuss the particulars. Sorry.
The best I can suggest is to make sure that you are participating. That “defending” a tower by yourself for much of the game may be a strategy you like to employ, but it is not necessarily a strategy that everyone will be on board with. Again, that isn’t specific to you, but it is a style of gameplay that I see a good deal of that can result in non-participation reports/data.