Validating a level means you actual test it out and have a solution. If you try to share a level that hasn't been validated this way then you're still able to load it, but you don't get the "VALIDATED LEVEL" text or the "GOAL" text in the top-right.
If you're curious, this level's share code is:
If you copied and pasted that into the game, you would be able to play it! There's still a few loose ends to tie up in terms of artwork as well as coding some new behaviors for existing tiles. I'm hoping to have this soon.