This paper doesn't comment on outcomes for patients.
No one is arguing that NPs or PAs don't know how to order imaging studies, refer patients to specialists, schedule a follow-up appointment, or check a box in the health record that they told the patient to quit smoking. This study doesn't examine the appropriateness of those things, which is where you would expect minimal training to hurt patients. This study is manipulative because it deliberately conflates doing the same thing as doctors on average with doing the right thing for each individual patient. If a doctor orders 5 appropriate referrals after making the correct diagnosis, that is not the same as an NP referring each of his/her patients to a specialist at random because he/she doesn't know how else to work their problems up.