I think it's important to break down what he's actually being charged with, and note he's not being charged with any federal offense under any federal anti-terrorism laws. The PATRIOT Act does not apply here.

What he's been charged with are first degree murder and second degree murder under the laws of New York State. First degree murder in New York only applies to several very specific circumstances, and the only one of those even remotely related to what Luigi Mangione did is:

the victim was killed in furtherance of an act of terrorism, as defined in paragraph (b) of subdivision one of section 490.05 of this chapter

Which is defined as:

(b) for purposes of subparagraph (xiii) of paragraph (a) of subdivision one of section 125.27 of this chapter means activities that involve a violent act or acts dangerous to human life that are in violation of the criminal laws of this state and are intended to:

(i) intimidate or coerce a civilian population;

(ii) influence the policy of a unit of government by intimidation or coercion; or

(iii) affect the conduct of a unit of government by murder, assassination or kidnapping.

The reality is the prosecutors want to be able to get him with first degree murder, but the likelihood of that sticking, I believe, is really low. I think they believe that too, which is why he's also charged with second degree murder. Second degree murder in this case seems like a slam dunk, whereas "charged him with terrorism" makes for flashy headlines but is just not likely to go anywhere based on what's publicly known in this case.