They missed the call. Because the refs weren't paying attention to the spot of the 2nd kick, they gave it to Seattle that the kick was behind the LOS and unlike a pass, you CAN double kick it... but the ball cannot go past the LOS. Because of the block, the ball didn't... until the kicker carried it past the LOS to do the double kick.
So yeah, they messed up, but man... whoda thunk THAT would have happened???
If it had been one of those crazy windy days like in Soldier Field and the punter kicked it and after going forward X yards, the wind blew it back, then the kicker would NOT be allowed to kick it again.
At least, that's the explanation we got.
Expect THAT to be a rule change come next year...