Held to standard of an RN

What exactly does it mean when a nursing assistant will be "held to the standard of an RN" after passing the NCLEX? Does it mean I have to act as a nurse if a patient were in distress, ie: applying o2, etc? Does it mean that I could also potentially be held liable if the patient's actual nurse missed something?
It means you must act in the same way an RN would be expected to act in the same situation. Since you have passed the NCLEX, you will be expected to act in accordance with the Nurse Practice Act in whatever state you live in no matter the position you are employed in.The facility may not expect you to do the job of an RN at CNA pay for example, but if trouble arises, you will be held accountable to the higher standard. It's something a lawyer can rip you to shred over if given the opportunity.

If you passed the NCLEX, you are no longer a CNA, no matter what your facility says.

My facility held health care techs/CNAs to the RN level once you were licensed by the state. At that point, you could no longer function in the support staff role.

It means you're expected to assess and respond to each patient you interact with as if you are working as an RN. Ie. entering a patients room to obtain vital signs, they're irregular...then not only is the RN assigned to that patient responsible for an intervention but you as well in the eyes of the state / law. I would not recommend continuing working as any other scope of practice other than RN after obtaining your license. Puts you and all your hard work at risk.