I imagine they word it like that because the profits from the sale itself count as income, if he mined those coins then he's talking about the risks he had acquiring the mining equipment, running it all and avoiding getting his coins stolen, and he's saying his cost basis is 0 because he didn't pay in cash for the coins. If he had, and bought at say 1000 and sold at 15000, then at least he would only pay on the profit of 14000 a coin, but in his situation he has to pay taxes on the whole amount he sells for.

I'm not an EU tax expert but I believe any wages made in the year would have still contributed to his wages including the sale of his coins, as someone else suggested he could have just sold less this year, but perhaps didn't realize the tax ramifications or was afraid of a huge drop in the price. Bitcoin has dropped around 90% in a very short timeframe in the past multiple times so I can't blame anyone for getting out while the going is good.