The biggest problem with articles like this is that the author says things like "the judge was biased" or "the judge sided with the defense" when, in fact, the judge was correctly applying the rules of evidence. Moreover, the prosecution has blatantly disregarded basic courtroom decorum and the Defendant's constitutional rights.
The possession charge was dismissed because a) under wisconsin law a 17 year old is permitted to carry such a firearm b) the law is so poorly worded that there was this enormous loophole, and c) the prosecution failed to make any valid argument against dismissing the charge.
The prior statements were not allowed in because under rule 904 (as in most jurisdictions) prior acts and statements are inadmissible to prove guilt. The only thing it can be used for is to establish motive. However, considering that his prior statements are not consistent with what happened and they were more of a general nature rather than specific threats.
Look, is he an idiot for being there? yes. Does he seem to fetishize the militia life? absolutely. Is he a hero? nope. However, the prosecution are the ones that have a burden to prove their case beyond a reasonable doubt, which is the highest standard in law. They have failed so many times. The only reason there hasn't been a mistrial is to let the public appreciate the spectacle.