I could forgive one photo. But when multiple photos in multiple stances from multiple angles show the same fault, you can be pretty certain it actually exists. You can't see his hooves very well in the photos, but they certainly don't look excessively long or imbalanced.
Calf knees are calf knees are calf knees....in Tennessee Walkers, Foxtrotters, Thoroughbreds, Clydesdales, and, well, calves. Excessive strain is placed on the supporting tendons and structures in every case (save for cattle, of course, with are naturally built that way), and those soft tissues are then prone to stress and tearing during even normal movement due to hyperextension. There's a reason that "back at the knee" is considered one of the worst conformation flaws when it comes to impacting soundness.
In fact, read this from a TWH website: The opposite condition to buck-knees is "back at the knees" or calf kneed (Figure 8). This conformation fault is extremely serious and many calf-kneed horses do not stay sound. This condition positions knees that are set behind or back in the horse's leg. Calf-knees allow the knees to bend backwards (hyperextend) and predispose the horse to unsoundness.FULL ARTICLE