This is a shitty watered down interpretation of nihilism. Just because you don't believe that ethics are governed by some higher power or are baked into nature, doesn't mean you have no moral compass whatsoever. Nihilists are not a bunch of serial killers.
This is the same lazy argument about atheists having no reason not to rape women in the street. You don't need God to tell you not to do that. You can have your own reasons to be a decent person.