Uncontested lineout mauls can be confusing for fans and players alike, because so many things are happening at once.
This video explains what the actual elements needed for a good outcome for the defense are: 1) ball transferred back too early, 2) no physical contact with the "not-yet-a-maul" pod 3) pod moves downfield and comes in contact with a defender, who is effectively obstructed.
If Larsen hadn't been run into, Thiebes's tackle would still have earned the Free Jacks a turnover. Great outcome for New England -- it went exactly as planned.
Game management guidelines tell referees to treat it as the ball carrier running into the back of his own player (so a scrum) rather than full obstruction (a penalty), which is why the sanction is a scrum to the Free Jacks.
Then we have a clip from Atlanta looking at why this tactic does not always pay off, namely when the mauling team notices and waits to transfer the ball to the back.
Technically Atlanta had too many men bound on to the ball carrier (the early bind called a "latch" is now limited to 1 teammate, a recent change) but you are almost never going to get that call as the defense when the other team at the lineout was binding up to form a maul. I've never seen it called in this situation -- only in open play.
Hope that helps to clear things up! If I got something wrong, let me know and I'll do my best to correct it.