As a rule only a psychiatrist should give a diagnostic.
Only as a discussion, both NPD and APD can share the traits you've mentioned. Also in some cases, someone might have a personality disorder and also have traits from another one (you could have NPD with APD traits, or NPD with Borderline traits for example) or share traits from one or more personality disorders but not "match" the diagnosis criteria for it/either.
The main difference would be that someone with NPD is very motivated to gain fame, admiration, the position in society they feel they deserve. Yes, some people with APD might want this things, but it isn't their main motivation.
Overly violent behaviour is more often associated with APD, though they can all be dangerous if you are perceived as a threat or that you somehow harmed them.
Many narcissists don't actually want to do any nefarious things to those that they didn't deem an enemy. Might be arrogant, might think they are way better than you, might be indifferent to your needs or feelings but they might not be at all interested in something bad happening to you. Obviously there are exceptions.
So, technically I don't know why someone with NPD would claim they could do nefarious things without feeling remorse given how such an affirmation is in general perceived by others,. Might be that they hate that person and are using it to intimidate. Might be that someone with APD likes to see others scared of him.
Just as likely that it is just a jerk who enjoys scaring others this way. Also, if he is a teen or even an adult in a criminal group (or one who opposes rules and praise aggressive behaviour)- might also be bragging.
Without a specialist examining him, you will never know if he has a personality disorder or is just an abusive person. I'd say whatever it is, you should be glad you are out.