One of Verdi's most memorable works, "La Traviata" is one of opera's most popular romantic tragedies. Pérez and Costello are playing the star roles of Violetta Valéry and Alfredo Germont - a courtesan and a nobleman who engage in a fiery love affair that is quashed by Alfredo's family. Violetta dies of consumption, and Alfredo's heart is shattered.In the context of the interview, calling Alfredo a nobleman isn't a big deal, but it is for understanding the opera itself.
If Alfredo were a nobleman, there would be no consequences to the affair. His father might have a quiet talk with him, reminding him to keep Violetta at least somewhat out of sight and suggesting he not spend every penny he has on her. And we'd have no opera, if that were the case.
But the Germont family is bourgeois and upright. Alfredo's public involvement with Violetta is causing a scandal back home, and interfering with the marriage prospects of Alfredo's sister. That puts the family in a serious situation; the sister has no chance of marital happiness and the entire family's social acceptability will be affected if the affair continues.
It's out of sympathy for the sister that Violetta agrees to leave Alfredo, while concealing the real reason. That's why we find the scene in Act III, where he throws the money at her, so wrenching. We know the sacrifice she is making, and why, and we know that she still loves him. It's why we love her.
Update: The interview now correctly identifies Alfredo's social status.