I guess my expectation when I viewed the screen is that the % full showed what percentage of seats available at the last home game were sold. In light of that expectation, I viewed what the screen actually displayed as a bug.
As Marin pointed out, it's not really a long-duration thing anyway (at max you're going to have a week to a week and a half where your shiny new arena is being used to calculate fullness of your old game). Just figured I'd report it, if y'all decide "it's a feature" I'm fine with that.