He had two things: (1) the right to make and publish a change to a project he controlled and (2) a mechanism (npm and its ecosystems versioning practices) to have his changes run on thousands of machines. Making changes via (1) is not an attack. Leveraging (2) to cause ‘damage’ is without question an attack, even if the damage is just burned CI minutes and even if the victims’ comically poor practices bear some (most) of the responsibility.