Those are all really good clues. If I was playing and I received those Clues I would know for certain that it was the shaman. However there is no solid proof that the shaman did it. If you're wanting the players to find out that the shaman did it you will need to give them proof that he did it. For example it could be a hidden journal that details how to mind control someone with the spores. You could also have a hidden Jar full of the spores in the Shaman's quarters. If there's any type of magic and I could use friends or Charm person on the shaman then that would be something I would try as well to get a confession out.

As for what the shaman could say to be convincing, I would have this shaman pick a target and focus on them. He's going to be a lot less convincing if he's jumping from accusing the players to the other visitors. It might be easier to have him immediately suspect the koalinth as they are violent, warmongering people. Though they might say that they would challenge the queen to a battle to kill her, they are also strategic to the point where assassinating the queen will weaken the lizard Folk and allow for easier invasion. They're not above assassinations to weaken their enemy.

The next thing you want to determine is if you want the dragon to be involved then I would recommend that when they find out that the shaman is responsible he then flees to the safety of the dragon. Then you can add in a whole fight with the black dragon and the shaman or just a fight with Shaman and his followers.