They are standing on a dune, not level ground. This is why part of the legs are behind greenery. If George is further down the dune, and Louis is near the top, George may look shorter and Louis may look taller
And looking at the composition, they form a triangle both around the outside of the group and internally with the linked arms, which means that the eye travels around the group. They may well have been posed at different levels to achieve that effect.
But, like I said, some commenters are so nitpicky they'd pick fly shit out of pepper. It must be ghastly being inside those heads. Imagine having to deal with them in RL....😒