There were a couple other passengers who I overheard mentioning that the bus was new. The driver didn't really seem fazed. Here's a couple snaps of the rear portion seating. Every other seat was "intentionally not in use" for obvious reasons.
Maybe those Chicago/Forest Glen swaps were in preparation for the Proterras? Best I can come up with. Swap ~20 old buses to Chicago so that when the new ones do come in they can just retire from there.