Bitcoin daily trading volume is over 9 Billions USD. He didn’t crash the market, but he definitely made things much worse by being grossly incompetent. Looks like he panicked and he sold most of it at the lowest point. He would have had a much, much better deal selling OTC from the start.
Further, the main reason for selling this comparatively small share of the MtGox BTC and BCH holdings (yes they own both now) was to pay for his fees and some of the MtGox Fiat debts. They still sit on over 160.000 BTC and BCH while MtGox customer haven't received anything yet.
On the bright side, at least those Bitcoins were distributed instead of being offloaded to a whale