What he spent was probably a tiny fraction of his stack.
Discussion
We don’t know that.
I guess regardless of the unit of account, USD/BTC or something else, a pizza would always be a relative small percentage of that unit, either from what he already had or from the cost of mine it, I find it hard to believe he would spend a month's worth of mining, or a large percentage of his stack for pizza.
I'd like to think he at least has a handful left.