Fake wall. Notice how its placed exactly right under the current ask. AKA he really doesn't want to buy any bitcoins.
That could easily have happened by accident. Here is how:
* One person puts ask at 10.65999;
* Another person tries to outask the first one and puts another ask at 10.65998;
* "Mr. M" comes and creates a buy order without specifying the price manually. Mt. Gox defaults to the best ask price, which is 10.65998. The order is partially filled, the rest you can see on the screenshot.
That was not what happened though, I witnessed it.