Opponent's time not running...
Technically his time would have ran out even if he used pre-moves for every move - each pre-move takes approximately 1/10 of a second to be played, so thirty of them would be played in 3 seconds > 2.7 seconds.
I used to think it was kind of cheap, but after reading Nakamura's book "One Minute to Mate" on bullet chess, I have found it to be a very useful tool.
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