I don't think it counts as training if he IS LITERALLY JUST WILDLY FLAILING HIS WEAPON AT THE GRIMM. The established threat of the Grimm is simply not there. They have yet to EVER be a significant threat in the story, with the possibly exception of the Dragon, but it was clear from the start that it was going to be Deus Ex Machina'd.
It was an analogy. What is it with the internet and people not getting argumentative structure? Water is an explosive with a trigger- electricity. Dust crystals are an explosive with a trigger- another explosion.
He isn't- I don't... UGH! He isn't stopping it's movement entirely- that's why it's resisting. If you latch onto the side of a boar, though, there's not a whole lot it can really do to immediately get you off, and he hardly needed long to stab it a few times. Most Grimm we see die in literally one hit, comparable to it's size. Shanking a Boarbatusk in its underbelly, where it was already established it is incredibly weak and which is also the natural place to do so in this case, would not be difficult.