In the not so distant future bitcoin will be 900$
then you will realize this is a buying opportunity and send your money back to the exchange
by the time your money arrives at the exchange price will be have double
you will still buy in, because you understand the market, and
because bitcoin. 
Spot on.
Also, "in the not so distant future" will probably be around late April/early May, so I also think Mat didn't pick the smartest moment to withdraw all funds. But let's see, if there's one consistent theme to his posts it's that he changes his opinions pretty quickly (nothing wrong with that, btw. better than being permanently stuck in either bull or bear mode, imo)
The other theme being his unrelenting and highly transparent book talking.