The end of the Fly action states:
If you’re airborne at the end of your turn and didn’t use a Fly action this round, you fall.
The target can walk on air as if it were solid ground.
This gives the target the ability to move through the air, but it doesn't specifically say it's a move speed. Additionally, if the target treats the air as solid ground, they wouldn't normally need to spend an action to not fall through the "floor."
My concern is that these two spells are the same level, but seem to function very differently. Does the Air Walk spell necessitate the usage of the Fly action, or does it literally allow you to stand on air?