No. Movement of bitcoin from a wallet address known to be owned by Mt Gox would not cause a bear market. The funds were only moved from one bitcoin wallet to another bitcoin wallet - that's not a sale, that's a transfer. A bear market could only be caused by one transaction if that transaction was to sell Bitcoin for a fiat (or any other) currency.
This is how supply and demand works.
That amount of btc can pretty much cause a best market if FUD got spreaded wide after that amount of btc has been sold. Somehow, it is quite scary for Mt. Gox address to send out btc. Probably the one who received it might have had strong connection to the trustee. Whoever he/she is, it would not be good if the one who receive those btc are someone who will likely dump soon.