As the Description tells already, execute runs each command, starting from the last entity in the list from an entity selector.

Steps to Reproduce:

1. (Empty world) Place down an armor stand and stand besides it
2. run

   say @e[sort=nearest]

   and it will print out <your username>, armor stand which is the expected behavior, you are nearer to yourself than the armor stand

3. run

   execute as @e[sort=nearest] run say hi

   and it will print out the armor stand before your username

Despite the order in the entity selector is correct, as seen in the first example, the execute goes through this list, starting at the back, which is not the expected behavior in my eyes.