That is true, always keep in mind that digital assets such cryptocurrencies are very volatile that it can get you rich quickly or make you poor in just a blink of an eye.
Buying bitcoin back when it was a three digit value in USD and selling today when it is five digit - I would not call that get-rich-quick nor riches in the blink of an eye.
It is more of a myth because altcoins tend to show that not bitcoin, but I dont think know much of professional traders who went from rags to riches trading altcoins. The most that people have been able to was to gain some and lose some eventually watching the altcoin die out.
But with bitcoin, you can never really make that mistake, buy it at low and you will be destined to profit in a few years. As with any other bear trend, those who bought at the last one between 2018-2020 are reaping a good profit at this price.