One is one worst than the other, both are (at least in my opinion) bad for the game as well as a whole for the community. With that said though one is just easier to catch than the other. All you need to do with toxicity is look at the chat. Did they say something toxic? Yes, the evidence in the chatlogs proves it.
Whereas trolling might not be so black and white. Any champion can be a "Support". Ive played TF Support for awhile, usually when i have a Jhin ADC as the Gold Card/Deadly Flourish is a great combo! But its harder to prove someone is trolling especially if they dont say anything in chat. You cannot prove someone is trolling just by looking at them. There could be any number of variables that might make it look like they are trolling:
They could be new to the champion, or new to the match-up they are currently in. They could also be New in general to the game!
They could be rusty for not playing for a long period of time, or also from recent changes in a patch.
They could be trying something different to see if it works.
The list goes on. But the main point as well is that Off Meta will never be a bannable offense. And at least from what i seen in your post thats the main issue you have. If you can go into detail to see what exactly they did that made it seem like a troll aside from them going off-meta we can probably get a clearer understanding as to what happen.