There is a huge difference here.
For Mister Sandmann, he and multiple witnesses stated they never threatened or insulted Mr. Phillips, and the video evidence proved that was the case. Of course, it did not help Mr. Phillips that he was proven to have lied in his claims, and had been lying about his background for decades, including being a Vietnam Vet (when in fact he never left the US, and was kicked out of the Army for multiple cases of being AWOL).
Now for this case, Nowhere did Mr. Hosinski make any claims like you asserted. He never said his daughter was threatened, nor has he ever stated that the minor threatened arson. He never made such a statement, and never presented that in court. And not a single witness ever said that it was done.
Notice, you are trying to accept a Redit post from somebody not even connected as "proof". Funny, how the teacher himself never made those statements. It is not up to us to prove that she was not threatened, it is impossible to prove a negative. It is up to you to prove that she was. And without even the person directly involved claiming that, you have no proof at all. Because if anybody would have made such a charge, it would have been Mr. Hosinski in court as a legal case even slightly for anger based on the making of a threat.
He did not make that claim, not a single person involved has made that claim. Therefore, it is only a figment of your imagination.