All my responses are truthful, no matter what setting. And I see professional as being truthful in a courteous way. I earned enough respect from my superior this way for her to offer me a job as a manager (which i gracefully turned down).
A person who tells the truth is trustworthy, but perhaps they could tell you were talking around it? I mean, they have to know that a person would leave under such circumstances for a better job. So maybe that was the reason for the question.
But my thinking is that no matter what job I have (low or high pay) I am going to do it as best I can, and I am going to be professional about it. I am going to learn it in and out, because who knows if the skills or experience gained from it will pay off later?
I used to work at a car wash. A boring old car wash. But I was offered more pay than others because of my enthusiasm. I started to dance outside of the car wash and wave at passing cars on the freeway. People started to come in saying "hey, I saw you on the freeway, so I pulled over. I need a car wash anyhow."
That same day, a car dealer saw me, and brought half his lot to be washed.
Embarrassing perhaps to dance in front of a store (which is probably what my co-workers were thinking)? To me it wasn't embarrassing, just one way to get the job done.