Why not? You make rivals, and then you are surprised they actually try everything to kill their rivals? Or are you saying that the hunter should not have done the favor, which would still leave many other ways to get rid of your rival early, like outing them to a wolfpack.
Yes, I'm saying the hunter shouldn't have done the favour. Johho only did it because he thought Nautilu could win with any team, and I gather Nautilu only sent the PMs because he also misunderstood the rule. If they'd known the actual rule, they would have bided their time and looked for an opportunity less likely to blow up on them.
Rival seer and apprentice is an obvious setup. Seer scans the rival night 0, and they both know where they stand. Instead the apprentice misread the rule and went crazy.
As for selling out your rival to a wolf pack, that's just stupid. Your team comes first, it's irrelevant if your rival is still alive if the other side wins. Patience is a far better approach. In fact... I've been an unclaimed apprentice and rival to the seer, and that's exactly what I did. Voted him when he was run up, but otherwise just let things get on with it. The odds are very high one or both of you will die anyway. Me in that case, with the seer going on to lead the village to victory.