the paper bag look still intact, even through the blur, i didn’t see the mailbox move at all either, Doesn’t seem to be the device location that has been explained based on info that i have heard on radio, etc.
I think what you are seeing behind the blur is bodies, not the bag.
Distressed people, fallen barriers, stains in street. This is the second bomb location, no doubt.
Mailboxes are “nailed” - screwed to ground.
Bottom of the legs would stay in place, rest up could be deformed.
Mailbox more than like is bolte down. there should be a fairly significant “dent” in the concrete where ever the bomb was placed, at least major “burn” marks from the powder ingnition.