they sure didn't use it LOL. Maybe the pole has tilted over time if it's metal... Or if the wood pole was renewed they may not have secured the arm on straight...
Yeah I've seen poles that are installed with another pole tilted at 45 degrees to keep them from shifting over time and more commonly see stainless steel rods that act both as a support and a ground for the streetlights and transformers. The pole in my yard has a stake in the ground with a wire that goes up the pole to the stainless stell support rods, the streetlight (well actually the tapered elliptical lag bolt), and the transformer.
Oh and it also has one of those Wi-Fi devices on it too.