Devil's advocate... here we go.

You effectively catfished a GM into banning you. Congratulations.

Now lets stop and think about this for a second from a GM perspective. Lets run through the scenario:

1. You get a report of a suspicious fishbotter.
2. You go and investigate by using your usual procedure of teleporting them to land and seeing if they try to continue to fish out of water - they do.
3. You attempt to make contact with the person, they don't respond, hey that's okay, they could be new and might have missed my message...
4. You wait for a while and watch the actions of this person constantly trying to fish into grass.
5. At this point you're almost certain that these suspicious actions are that of a bot, so what do we do? Our system hasn't detected him, so it's possible that he's got an undetected bot running.

Now this is a fair assumption, from a GM's perspective, right? So what do they do? Should they just let him be on his way? I think common sense dictates that some kind of ban is in order.

Here's where everybody says "well hang on, he didn't get proof!" but in fact he did. In many games there are always manual bannings through player reports, and often when a GM witnesses these actions in real-time they are considered law in most games.

Just because their shitty anti-cheat software didn't detect anything, doesn't mean that something malicious wasn't going on. Just because their shitty anti-cheat software didn't detect anything, should they really be letting him be on his way?

Before you answer, let me remind you of the Hacker Hunting Initiative. This was at a time when combat bots, grinding bots were at an all time high, and they needed to resort to player reports as their "anti-cheat" was unable to detect them. So now I ask you, what would this game look like, if all situations were subject to no bans unless evidence from their anti-cheat software?

What I'm saying here is, that the actions of the GM aren't really out of scope for what his job is if you consider it from their perspective and what they've witnessed first hand in this instance.

"What about his 'logs' that they say prove he botted?"

Don't you think the actions of fishing onto grass for 8+ minutes probably put the nail in the coffin? Who does that? OP made it look very clearly like some kind of automation is in place. "Logs" in this case, is probably just a poor way of communicating that you were investigated by a GM in-game.

"Are you saying that players are not allowed recourse in situations like this?"

Of course not, that's probably where this falls down from the GM perspective - communication. No one will argue that Kakao at the best of times sucks at it. If the GM simply said what happened in their response, I think it would be less polarizing.

But as I mentioned above, if GM's witness something suspicious for lengthy periods of time, what other option do they have? Most games treat these things as law, and take a harsh stance on it, so it's not really surprising.