Can you elaborate a bit on why it's a weird response? What would be more appropriate? Non-native speaker here
It’s just old fashioned. If you’re on this forum you’ve read enough English you’re unlikely to mess up but
How are you?
Great thanks. You?
Fine, fine.
It’s scripted insofar as no one cares how the other person actually is and answering I anything other than a positive fashion would be a faux pas but everything after “How are you?” is fluid. You can also go even less formal, e.g. “How’s it going?”