The red coat did a shady thing. Alternative flights and compensation amounts should be discussed with and accepted by the passenger before any change is made. The red coat put OP in an awful spot by taking him to another gate and just telling him to get on. The assertive among us would have put a stop to the process there, if not earlier. By silently boarding the plane, OP allowed the red coat to prevail, and implicitly agreed to no compensation. It's a shame to see unassertive passengers thoroughly taken advantage of, and this red coat is going to continue to pull the same garbage.

Oversold flights are the GA's problem, not yours. As much as you may want to help the GA or the other passengers speed up a departure, look out for your own interests because a harried employee may not. It is perfectly reasonable to force a discussion about alternative flights, seats, and compensation before giving up your seat, no matter how reluctant the GA may be. Trust me, when the GA wants to get the flight out quickly, you'd be surprised how quickly they can print you a voucher.