How does unique character dialogue trigger?

I’ve wondered this ever since I started playing the campaign. When I was playing El Dragon on Algoritm, he didn’t say anything at all but when my buddy played him in the same level, he had like four to five moments where he spoke directly to Isic. Same thing happened with Phoebe in The Renegade where she flirted with Caldarius. Do you have to do something to activate this dialogue like completing lore challenges or is it just random? I feel like I’m missing something.

Use Deande or Orendi and play Void’s edge… Stay around the sentry when he gets to the stairs… Buy an upgrade… See if that works… Post here again and I might have another one…