Before reading other responses:
Ali has moved a card into his hand, when the game rules did not allow him to do so. He has committed Game Play Error - Drawing Extra Cards. This particular infraction has been the subject of a bit of policy editing recently, so it's good to check what's currently in the IPG.
Since the scenario did not specify, it's safe to assume that the identity of the top card of the deck was not known to both players, and it was not drawn into an empty hand. Additionally, this isn't reasonably the result of an “legally resolved illegal instruction” (though that phrase is a bit complicated…have to check the AIPG), CPV, nor resolving the stack in an incorrect order.
The one sticking point is, was this a “confirmed” draw? If it is, the correct fix is to consider a backup (which means taking a random card from hand, putting it in the deck just under the Top), or leave the game state as-is. If it's not, the correct fix is to reveal Ali's hand to Ned, and shuffle a card of Ned's choice into the random portion of the library (i.e., not the top 3 cards, likely).
On investigation, we find that, when asked about a card draw, Ned said “Yeah, no effects”. Furthermore, Ned said this while not remembering his own Spirit was on the field - i.e., Ned believed his statement would be followed by a card draw on Ali's part, and Ned's statement could reasonably be understood by Ali as a confirmation. I would rule that Ned “confirmed” the draw, and I would authorize a simple backup here - Move the Divining Top from top of library to battlefield, tapped, select a random card from Ali's hand and place it on top of the deck. The game is now in the middle of resolving Divining Top's ability - Ali doesn't draw a card, then the Top will be placed on top of library.
Ali receives a Warning. Ned has committed no infraction. (Unless it's actually FtMGS?). Continue the game.
After reading other responses:
Ned has probably committed FtMGS here.
Originally posted by Michael Warme:
Ali received confirmation on the draw, so it is NOT DEC
I believe this was the case in an older version of the IPG, but the current version does not indicate that the infraction is different. It's still DEC, still a Warning.
I believe the correct backup would back up to the point of error - the card draw during Top's resolution. So, I wouldn't backup to before the Top was activated, I think a backup would effectively put a random card from hand into the library under Top. (which, realistically, is no extra information for Ali, who has almost certainly been activating Top's first ability). So, I believe a backup is justifiable here, it doesn't open up extra lines of play.