~but he quit selling artworks and other little businesses that kept him going he stopped, he now depends fully on Bitcoin.
Why he must quit selling artworks? If he only invest in Bitcoin, it won't spend a lot of time. Even he invests and trades Bitcoin, I'm very sure he still has enough time for selling artworks and running his business. It makes no sense to solely relies on Bitcoin, especially Bitcoin investment only. It takes for few years to take profits. If he has no regular income from his jobs in real life, how he can fulfill his daily/weekly/monthly necessities? 
Bitcoin is the king no doubt, but From my Point of view I think that depending fully on it might be risky to you financially. I don't recommend anyone to depend solely on Bitcoin or any single asset. Bitcoin can fluctuate rapidly and market volatility might impact your financial stability. It is actually very risky to invest in a single asset.
It is better to diversify assets. And we should have regular jobs even if we have assets. Sure, Bitcoin has high volatility, it is also a risky investment. It will be riskier if someone invests in Bitcoin with no proper knowledge. Your friend is one of the real example, if he just join Bitcoin investment now, it means he buy at an expensive price. It is totally not recommended for a beginner to start their Bitcoin investment in the bullish season. Even worse, it is almost the end of bullish season.