It's important to note that last time, the poker players beat CMU's AI by around 500k chips as well and they had the gall to declare it a "statistical tie". Yet if they win by chip they will claim to have "won".
which is: "If after 120,000 hands either Libratus or the humans are one standard deviation above break-even, they will have won the competition with “statistical significance.”"
(I'm a professor at CMU, but I have nothing to do with this research or competition.)
To your point, I wonder how they account for mental and physical fatigue. To a computer it makes no difference to play thousands of hands over such a long period of time or hundreds of hands over the course of a single day. Humans on the other hand don't have the same attention span as a computer.