Yes. Loved this movie. Go watch it.
If the bus story is true, the responding MIB were close on hand, and swooped in converging for the climax, only to shrink away immediately after spraying the evidence off the road.
Practiced. That's the word that comes to mind. Routine.
My red flag is access. They're going to control access to the scene first and foremost, IMO the bus would have never made it to the scene, it would have been stopped by someone dressed as state police for an accident blocking the road ahead that would be cleared up shortly.
And that's why this random armchair cowboy don't believe the story. You don't conduct a routine professional cleanup like this, in less than an hour, without the basic first commandment of keeping the scene safe by blocking access.