Yeah you should have given them advice on how to land a gig and not diagnosed them with NPD. I see where you're coming from and I agree it might be useful for OP to work on how they communicate, but that should be between them and a therapist.

There are a few assumptions that are false. For one, I am not a doctor, and this is not a diagnoses. It is explicitly an opinion based on (very) thin evidence. I agree they should see a therapist, if possible. I would not normally be so blunt, but the OP asked.

But the primary false thing I want to address is the tacit assertion that "Telling someone they have NPD traits is a personal attack." I understand that assumption because, sadly, accusation of personality disorder has become a common style of personal attack. It's very similar, actually, to the classic status of "homosexuality" - once a pejoritive, now mostly just a fact. And I'm not sure if you noticed, but HN has a LOT of psychology-related content. As a group people here seem to show a lot of admirable compassion and empathy for each other's vulnerabilities. I think it's a remarkable feature of the place, and I hope you can take my words in that context. NPD is quite common in the world, in our field, and its entirely posssible to be a good person who struggles with NPD.

Your protective instinct speaks well of you! But you may need to reassess whether or not I actually attacked the OP, given his request and the context of my response.