This is not accurate with respect to the federal ruling. The judge is not disputing the murder.*
"Murder" refers to an offense under any number of legal provisions, most of them at the state level. Nearly everyone is at least passingly familiar with at least first-, second-, and—since Chauvin—third-degree murder. Many are also familiar with the concept of felony murder.
Nobody is disputing that the premeditated killing alleged in this case legally constitutes murder under New York State law.
Instead, it does not constitute murder for the purposes of 18 U.S.C. § 924(c)(5)(B)(i) because the underlying federal offense—stalking—is not a crime of violence within the meaning of 18 U.S.C. § 924(c)(3).
That statute defines a crime of violence as one that "has as an element the use, attempted use, or threatened use of physical force against the person or property of another" or "that by its nature, involves a substantial risk that physical force against the person or property of another may be used in the course of committing the offense" (emphasis added).
Physical force is not an element of stalking, nor is there a substantial risk that physical force will be used in the course of stalking, even though it's not altogether uncommon for stalking to lead to acts of violence.