He "handed custody" over to the responding LEO, the LEO let the security guard walk.
Oregon does have "citizen's arrest":
133.225
Arrest by private person
(1) A private person may arrest another person for any crime committed in the presence of the private person if the private person has probable cause to believe the arrested person committed the crime. A private person making such an arrest shall, without unnecessary delay, take the arrested person before a magistrate or deliver the arrested person to a peace officer.
(2) In order to make the arrest a private person may use physical force as is justifiable under ORS 161.255 (Use of physical force by private person making citizens arrest). [1973 c.836 §74]
HOWEVER, he did not have RAS let alone Probable Cause (required, see above), and the security guard did not have to show a CHL or prove anything to some guy on the street.
Technically he was right that the security guard, to carry loaded in the city limits of Portland needs a CHL or must OC unloaded.
He didn't appear to illegally detain the security guard (ie keep him from leaving by threat or force), I don't know why the guard voluntarily stayed in the encounter.
The guard should have told him to pound sand and walked away, and if the guy tried to detain (again, no PC) he would be up on illegal detainment (kidnapping?) or assault if he held the guard by any force.
Schrödinger's cat paradox: security guard; legal with CHL, illegal without CHL, doesn't have to show/prove CHL to guy on the street. Guy has no RAS/PC. Guy was wrong.