It'll be as informal or as formal as you'd want it to be. The management is pretty inappropriate and unprofessional, so use that to your advantage. It won't be much about your past experience, but more so of them hypnotizing you to believing the "golden days" of CME is still a thing.

I showed up to the interview having exchanged an email thread for the open position of Customer Service. When I got there, the Senior Manager at the time started interviewing me for a sales role. He had forgotten what I had come in there for.