It's not clear what was done with the US$40k that was stolen but is it possible (likely) that they were used to buy bitcoins with to allow the bitcoins to be withdrawn thus driving the price up yesterday.
i.e. the hacker sent US$40k to some dummy account, immediately converts to bitcoins at whatever rate is available (pushing the price higher), then withdraws the bitcoin.
So this hack might have resulted in some "false" buying pressure. The hacker bought the bitcoins not because they were bullish about the value of bitcoin but rather because it is the most convenient and anonymous way to withdraw the money.
No, limits on Bitcoin withdrawal/USD withdrawal are 40k each. Even if the hacker converted the $40k to bitcoins,
(1) It wouldn't account for the whole volume of the rally yesterday (20k from 7.25 to 7.9)
(2) He could still only withdraw 40k BTC, so he might as well not touch the dollars...
(3) The dummy account would have to be verified.