The quick answer is that the "other" thing that floats up is just there for show and you don't need to worry about it.
In detail, though: Technically it is a reflection of how much satisfaction the visitor is getting from that expansion. Higher-tech expansions with high appeal should generally result in higher numbers here. But the easiest way to watch and control this is through the expansion editing interface that actually shows the appeal level, and by watching the satisfaction level in a given ship's happiness/interest display. The ideal appeal level is discussed a lot in other threads, of course.
So, does this number not interact directly with how much "filling up" a customer does?
Here's how I envision it:
Customer A arrives wanting 60 points of social satisfaction.
He sits down at the Singles Line and pays out $12 for 12 points of satisfaction. So, after 5 tics (or is it ticks), he'll have paid $60 and sated his 60 points of need. So, he leaves.
But if he sat down at a different Singles Line and was paying $12 for 10 points of satisfaction (because you adjusted the appeal settings,) then you would net $72 for 60 points of satisfaction, a profit of $12 over the other example.
Am I far off-base, Stay?