From the patch notes;
The first sentence, "In cases of spamming or harassment, a mentor can kick", seems quite clear about what you can kick people for. Unless I am somehow missing something, spamming doesn't in any way cover talking about game content, nor is that harassment. Spamming, a definition; the use of electronic messaging systems to send unsolicited messages (spam), sending the same message indiscriminately to (large numbers of recipients), especially advertising, as well as sending messages repeatedlyRemoving Players from the Novice Network
In cases of spamming or harassment, a mentor can kick another mentor or a new adventurer from the Novice Network channel. Kicked mentors cannot return for three hours, and kicked new adventurers for thirty minutes. Please be advised that, in doing so, your name, the name of the player being kicked, and the reason will be displayed to everyone on the channel.
* Customer support will be notified when a player is removed from the Novice Network. If your decision to kick a player from the channel was found to be inappropriate then you may face punishment.
* Mentor privileges may be revoked for repeated infractions.
In this case the players were chatting about a valid topic in the game, not spamming, nor were they harassing anyone, at least none that were mentioned by the OP. The OP chose to see their use of the Novice network to chat among themselves as 'spamming', but I don't see how chatting meets the definition of spamming.
Then there is this point, " If your decision to kick a player from the channel was found to be inappropriate then you may face punishment.", which makes it quite clear what will happen if you kick someone wrongly.
I feel sorry for the OP, and agree that the ban is harsh. I actually agree that the player's chat was inappropriate for that specific channel. But the players were not spamming, they were not harassing, they were not even flooding the channel, they were simply chatting. However, technically, it was kick abuse, and because the other players reported it, the GM was left with little choice.
I believe they are called Linkshells.