"MTGox is selling" is just a new kind of FUD, and some people are trying to manipulate the market with this FUD. They want other people to panic and sell their coins low, so manipulators can buy them and sell later. People shouldn't care about minor news, it's a good way to lose money if you trade by reacting to them, instead people should have a good long term strategy that ignores minor fluctuations. Time has proven that all these hacks, government bans and other stuff doesn't matter in the long run, so people should never panic on this market.
But is it proven that it is "not FUD" though? If coins from the trustee's wallet truly moved then what do you believe was he doing besides selling those coins? Plus how would you explain the dump in the exchanges?
At any rate, buy the dip.
one word: Panic
the cause of the panic has never been important. it can be anything and it changes every now and then. for example around $14k until $9k the panic was because of a lot of FUD saying "{blank} banned bitcoin". the {blank} was a lot of things including Facebook,... and different countries. I even heard "Japan banned bitcoin" among them
before that, last year around $3k-$5k it was the "anybody can spend your coins because of SegWit" FUD.
before than it was "bitcoin is gonna split and die" FUD
among these there were all the spam attacks against bitcoin and the scaling drama.
before that around $1800-$2500 it was "Bitfinex is pumping bitcoin, tether is the only reason it is rising" FUD
before that around $1200 it was the "bitcoin is a bubble" FUD and "this is like 2013" FUD.
before that around $700 it was "Bifinex got hacked and hacker is dumping all the coins" FUD
before that it was "China banned bitcoin" FUD.
before that it was "Bitcoin is a Ponzi scheme" FUD.
before that around $20 it was "bitcoin is a bubble" FUD
.....
each of these caused panic and investors dumped their bitcoin and caused the crash not any imaginary dump by one person like the Mt Gox trustee in this case.