So where does the capital come from?
Who cares? It's not the theme of the topic.
He told as a very basic truth that when it comes to an appreciating asset like bitcoin, investing more will bring more profit. There's always risk but those who invest know about it.
To be honest, many people have capital lying around, but they don't want to take any risks, even small ones.
What is important here is that you shouldn't focus on saving fiat money. Save in appreciating assets.
Now, talking about bigger capital, higher returns, that's more possible with bitcoin. But if you do it with other coins, I doubt if you can still be as profitable like bitcoin. Don't just invest, but always invest for long term, and bitcoin is a perfect example for that.