Revealing mistake: It's very clear they blew up a model of the buildings. The grass seen just before the explosions is way too long and is not as long when the characters are running away. Further, the truck and the barrels have disappeared at the explosion shot.
Revealing mistake: When Grady & Earl blow up their first graboid, one of the pieces of orange goo that hits the truck flies in from the LEFT. All the other pieces of orange goo get flung in from the right.