Actually, this is not true. If you've ever heard of "leading looks" then this is the perfect example. His eyes look towards the landing, crop it to the left and you lose this. To the right, and the trees are unnecessary and distracting. Here, you can tell exactly were he came from and where he's going. It's good you know about the rule of thirds, but it's definitely not the only rule of composition
The rule of thirds is definitely a rule that's meant to be broken, but your "leading looks" thing doesn't work because the goggles block is eyes. If the trees on the right are unnecessary, then why not crop them along with that distracting green bush at the bottom? The thing I do like about the composition is that the brightest spot grabs my eye, then the trees lead me straight up to the rider.