I could have feigned ignorance and not even brought up the issue with the attendant, however that didn't feel right. At least the attendant was honest about his expectations and I wasn't particularly put off by that. At least I got to spend some quiet time in the lounge and had already had food and drinks in the Flagship lounge.
It's absolutely your prerogative not to be put off by the attendant's expectations. As someone who tips in the Bridge, and likes the staff there, I'm shocked that one of the staff would actively communicate to you that tipping them is a condition of service, or to allow you to think so and not correct you. It's unprofessional, and is probably grounds for disciplinary action. I imagine AA would be none too happy with Sodexo if they found out Sodexo employees were not providing a service that AA is paying them to provide to its premium passengers because the passenger didn't have cash to tip them.