Years ago, prior to BK, I applied a few places and went through NFCU because they had the best rate and then went to the car lot. When I told the salesman my rate he asked if I'd allow them to try to get a better rate and I said sure but dont waste my time if you cant do it let's move forward with my NFCU approval. They beat the NFCU rate and I left in a newish car.
I should have just let them run everything and tell me what they could do before I told them about NFCU but live and learn.
IMHO you did it right.
They most likely ran your file thru different lenders, getting back multiple offers. They are sales people and work on commission, so they could have just shown you a middle or high rate offer. And who knows, in the end, maybe they did still withold the lowest rate. But you at least gave them a goal to beat.