The first bitcoin was not purchased, it was mined by the creator Satoshi, it is called the genesis block of bitcoin, after the genesis block was mined, people and devs that supported Satoshi started mining BTC
and giving out free BTC too, it was easy to do so then as CPU's could even mine bitcoin, not now that you need machines with a lot of computing power like GPU's. The block reward then too was ~50 BTC, so a lot of it was circulating, but it was not worth anything and people were not using it to make purchases.
10,000 BTC for two pizzas was the first time BTC was used to make a purchase, which was bought by Laszlo Hanyecz, it was easy to get/mine bitcoin then, so it was easy to spend 10,000 of it on two pizzas. But with time bitcoin became more popular, liquid and expensive to mine, and even though the block rewards has since halved to ~ 6.25 BTC (block rewards half after every 210,000 mined blocks) the hash rate is still
pumping, even to an all time high, which shows many miners are still competing to validate blocks, making the network secure and decentralized.
pizza for bitcoins? 
