Surprisingly, the truck wasn't actually that important. It did help block John's view. But Sherlock didn't jump into it as some people had theorised. He wasn't replaced with a lookalike from the truck. He didn't even mention the importance of the truck, and whilst it's a lucky coincidence if it was there by mistake, it was more there for obstruction than actually furthering the faking. A lot of fans were certain he'd jump onto it. Feel free to say "Not the way I'd have done it."