It's lame as hell for the instructor to ask to roll light and then do that.
If you came into my gym, I would probably go hard after you too. But not in a way to try to injure you. I would just figure that you were a big competitive brown belt dedicated enough to train on a trip so you were seeking a challenge. I'd roll hard but wouldn't crank for injury.
And I sure as hell wouldn't say "let's go light" first. Actually I'm going to start making it a policy that if a visitor asks me to go light, I just get up and refuse to roll with him. I'm just sick of the awkward shit that results when he inevitably explodes hard as hell his first opportunity.