hacking live chess?

If he "used all but 2 seconds", that means he had only 2 seconds left.

I think you meant to say that he had used only two seconds for his first 10 moves.

With pre-moves that doesn't seem impossible.

Premoves are a form of unconditional move allowed in live chess.  You simply show the server your next move by moving the piece.(Your opponent can't see your premove.)

It is helpful in endgame time scrambles when moves are forced or when pieces are so reduced on both sides that nothing can prevent a move. For example, in a king and pawn versus king endgame, your pawn breaks out and nothing can stop it. You know that you want to move h4, h5, h6, h7 and h8, getting a queen, regardless of what king moves your opponent may make. After each of your opponents moves , the chess.com server will execute your premove, charging you only 0.1 seconds for each move. Or in a queen or rook and king versus king endgame, you put your opponent's king in check and if he has only one move, you might plan your next move accordingly. If you are put in check or some other piece prevents a premove from executing, it simply goes away and you continue to move as normal.

Some people use them in openings. They set up a fianchetto and castle, and set up a hedgehog for example. In the opening, they know that their opponent will probably not interfere and they can reel off 7 or more moves without thinking. You can enter up to 5 premoves at a time. 

https://support.chess.com/customer/portal/articles/1444864-what-are-premoves-and-how-do-they-work-

You likely had a spotty internet connetion.

In Japan? Doubtful.