He could still have plenty of BTC in his savings.

He spent almost everything, apart from single-digit change. So NO, he doesn't have 'plenty of BTC' in his savings.

Source:

-snip- Other than a little bit of single digit change, I spent everything I mined. -snip-

How could he spend thousands of those Bitcoins? By buying a pizza factories? Cheesy

Back in the day Bitcoins were barely known by anybody and were worth, well, not much.

Oh yeah, that's true. The value of Bitcoin is not that high in that day Cheesy

So both of those person (pizza buyer & seller) must be regret it