That looks like the upper decks of a parking garage where the busses are located. I don't think the busses could be parked there due to low clearances common in most parking garages.
Your point of course still stands that the busses could have been staged and used, just not where you have them pictured.
I think they could have been. I saw aerial photos taken today and they showed the huge military transporter trucks from the convoy parked on the roof today. They are the same size as buses.
But I don't think this is your average parking garage- it's probably higher. They accomodate lots of bus excursions to games and even RVs that would need to get into the garage due to their lack of extensive ground-level parking.