Actually, it is not the fact that he sold, it is that he sold everything (apparently re-bought 1 btc later, which should have already brought it would probably bring him back to the same 40K).
Sometimes, when you cannot handle it, sell some, like 0.1% or something to release some steam.
BTW, in a grand picture, any sell might eventually look stupid. If btc is 1mil, 33k would look like a pimple on the chart.