The difference is that at a party like that the people are public persons and used to being recognized. Many of them are probably business partners so he is essentially using his assistant as a CRM to do sales.

Big agencies have entire dossiers on their clients for the sole purpose of brushing up on your info before a meeting so they can come across as super friendly and high touch. Even your hairdresser probably does this.

Main difference being that it isn’t creepy to keep track of things you can’t remember when being friends with hundreds of people is part of your job.