A precise transaction of 249.999 BTC is something very unusual.
Well, actually there are also 299.999 and 199.999 transactions there too.
And yep, I'd say the same. Somebody (person, institution, consortium, whatever) is accumulating. And the 0.999 part most probably comes from deducting the withdrawal fee by the exchange.
this has been going on for a while actually. I have seen many cases of this recently which is why I mentioned the possibility in my above comment. there are many big transactions like this and when you follow them back you rarely find any of them link to an exchange wallet which proves this new sneaky way of accumulating bitcoin without letting the market find out about it and go up.