Right character is acting like online replies where they didn't even really read the original. I mean, they read it, but they're just reacting without really thinking.
Yeah it's like "reacting" to live content (a human conversation) while it's ongoing. The joke is bro is acting like an anonymous member of the chat (chorus or peanut gallery, for my fellow olds) in a face to face convo, which is not appropriate.
I have actually noticed this trend of people of youth making little chirps or ironic barks (to use vg nomenclature) under their breath while a conversation is ongoing. This isn't totally new ofc, it's just my generation would be more like "uh huh" "yeah" "oh totally" as non-interrupting encouragement, but not so much with the ironic riffing.
I think it's kind of funny, but like anything there's a time and as place