Is it easy to manipulate the market, though? I don't see any dramatic changes over the last 24 hours in terms of the price of Bitcoin. Do you? Maybe the guy just got lucky rather than prevented the loss. It could be just a coincidence like some have rightly pointed out.
Oh, not to mention that even if it had an impact, it was 'local', not 'global'. The bet was about Bitfinex, and pouring $5 million worth of coins made the price, what, like $50 more for an hour on one major exchange? That's not an example impact or let alone manipulation to me. I think it actually shows quite the opposite: how much effort a millionaire has to put to make a tiny difference (if any at all).