He’s Being Followed
Everything was fine as they drove away, and Oliver was relieved to have the stone in his possession. Then he sees that a black van is following him. Is this a mere coincidence? Oliver took the same route three times to be sure. There was still the black van following him. Obviously, this is bad news.
He’s Scared
If Oliver stepped on the gas, the van would shake, but instead, it accelerated. To put it mildly, Oliver was terrified. Momentarily, he considered breaking the window and hurling the stone outside. Something, however, prevented him from following through.