According to ChessVibes (HT: Ken Regan) Hikaru Nakamura had 25 seconds left on his clock to make his 40th move, and claims to have asked the arbiter if they had reached the time control. According to Nakamura, the arbiter nodded his head, so Nakamura got up to get some orange juice, only to come back and be forfeited. Needless to say, Nakamura filed a protest, but as no one else saw the fateful nod (and obviously neither the arbiter nor Vallejo [if he saw it] felt like admitting anything) it was denied.
So did Nakamura get, well...the short end of the stick and treated unjustly? IF the arbiter did nod "yes" and then denied it, he deserves to be excoriated and should be barred for life from anything having to do with FIDE chess. (Having him make financial reparations to Nakamura wouldn't be a bad idea either.) However: According to FIDE's laws of chess, Nakamura had no business asking the arbiter anything in the first place:
13.6 The arbiter must not intervene in a game except in cases described by the Laws of Chess. He shall not indicate the number of moves made, except in applying Article 8.5, when at least one flag has fallen. The arbiter shall refrain from informing a player that his opponent has completed a move or that the player has not pressed his clock.
The bottom line is that Nakamura's loss, while unfortunate and altogether undeserved from a purely chess point of view, is ultimately his own fault.