Here's the difference between trolling and nonmeta
The intention.
The intention of a troll is to make people mad and mess others up and to throw games on purpose. The intention of a nonmeta player is to play the game just like it is for other meta players.
Let's take the concept of duo mid. It can be both regular nonmeta and trolling.
This would be trolling. "I'm going duo mid because last game I was arguing with this Lux and now she's going mid this game. I'm gonna go duo mid just to make her mad because I hate her."
This would be nonmeta play. "I'm going to go duo mid because I am the best at mid out of the 5 lanes, and I want to be playing my best role and bringing the best to the team, I am willing to work with the other mid laner to make it work and I will roam to help other lanes too."
Meta players can troll too. For example, you could play a completely meta Caitlyn ADC, but if your goal is to make your team mad on purpose because they didn't want a Cait ADC and wanted MF and you're purposely picking Cait just to spite them and make them mad, you're still trolling. If you play Cait ADC when your team doesn't want you to play Cait ADC and wanted MF instead but you're still gonna play Cait just because you want to play her? That's not trolling, that's just wanting to play a champion and you have the right to do that. It's the intention.
Ask yourself: "Am I doing this just to make people mad, or do I really believe it can work?" If you said yes to the first one, you're a troll. If you said yes to the 2nd one, you're a legit player. "Am I playing this champ/role to say a silent fuck you to my team?" If yes, you're a troll. Even if it's a meta role/champ.
If you're saying that it's hard for Riot to determine trolling or not based on intention... 99% of the trolls would also be saying something verbally abusive in chat so you can tell that they're trolling. Like for example "I'm just gonna go jungle and not help out. Open mid, just surrender." (a lee sin said that yesterday). That is trolling, that's why I reported him.
If he just wanted to farm jungle and just farm up for some more items before joining teamfights, that would not be trolling.
