Should he be arrested at the next NH primary for his knowingly false statements and their relationship to an actual bomb threat? Probably not, so probably this law is illegal.
Only 23 states have criminal defamation laws. The problems with defamation being criminal is what the article is about.
It's annoying to always use Trump, but it makes sense to use the person in the position of President to demonstrate that the law without discretion would net big fish.
IMO, law enforcement/DA discretion is ALWAYS a violation of civil rights. Laws would be less prevalent and less severe if they had to be applied equally. If you go through the mental exercise in obvious cases then you end up with a model of how the American System achieves discrimination through populist control of the executive branches and discretion, bypassing constitutional equality for minorities or the otherwise unpopular.
I'm not sure why you are interested in civil defemation law.
But coming the original question is whether this is on topic. Yes it is.