In my personal experience this has been common too, when I mix playing against 2500 players and 1900 players in blitz (I am 2350fide), it is relatively easy to skip over simple hanging pieces for a move or two.
In a regular tournament game it has happened a few times as well (one player commiting a gross blunder and other not noticing).
The big question whether it is out of ordinary statistically speaking.
Most top players would comment (as Anand and Carlsen did after the game) that double blunders are relatively common in top level play.
Here is one famous case: http://www.chess.com/article/view/the-amazing-chess-illusion
In my personal experience this has been common too, when I mix playing against 2500 players and 1900 players in blitz (I am 2350fide), it is relatively easy to skip over simple hanging pieces for a move or two.
In a regular tournament game it has happened a few times as well (one player commiting a gross blunder and other not noticing).
The big question whether it is out of ordinary statistically speaking.