It’s similar to how a lot of these things are done, the original elements are always bound to show more information than what would be seen on a print. On the 4K release of the Charlie Brown Christmas/Halloween/Thanksgiving specials, the widescreen versions show more information on the sides than on the also provided 4x3 versions. Sure the animation in this movie was digital but once again, framing from the elements always differs from what’s seen in the final product theatrically and home video. The extra information on the sides of the trailer wasn’t meant to be seen in the final product.