Well if you are wealthy already, there is not much risk in buying cryptocurrencies because even if the price crashes you have money already, and if the price surges (which has been the case so far) you're better off than before. So it's a low risk-high reward situation, no wonder rich people are investing.
Risk is based on how much per cent of your capital you put into Bitcoin. In other words, it doesn't matter if you have $1 billion investment capital, or just $1000. If you put 90% of your capital in Bitcoin, again, regardless of the total amount your capital is worth, you'll be exposing yourself to insane risks. If you just decide to go with like 25% of your capital, and your investment turns out to be absolute trash and you lose everything (won't happen with Bitcoin, but for example purposes), you still have 75% of your capital left, and from there don't suffer that much of a blow. It's just a matter of logical thinking. Other than that, this article isn't pointing at anything new since it's happening on a global scale. I think nowadays the fear of missing out is playing a very important role. People knew Bitcoin already, but just didn't take it seriously due to their stupidity, and now they see how much development this market has gone through, they start jumping on board.