The offer to move you to first class was based on two reasons, good PR and to make their flight easier. Less trudging back and forth with every one contained comfortably up front.
Should have treated it as a gracious gift, as all costs to carrier were fixed regardless of where you sat. The surprise benefits would have been mutual.
That may be true. However, the incident for me represents more of a quirk of human nature than anything else. Neither we nor the other passengers had paid for first class; therefore, none of us deserved to receive it.
I did, one time, fly first class. That was because I had arrived for an overbooked flight, and I was traveling on orders. I had to wait until the last minute for the flight crew to find me a seat, and that seat just happened to be an aisle seat in first class. To compound the situation, the woman in the window seat asked if I would mind trading, since her husband was in the aisle seat in the next row up. Oh, break my heart--first class AND a seat with a view, all for the price of coach! (I like sitting next to the window; it distracts me from the fact that I'm in a small, crowded, enclosed space.)