Sometimes Bitcoin also shows crazy volatility! And altcoins are still a more dangerous investment for me personally, but you're right, security is very important.
If you still consider investing in Altcoins dangerous, then stay away from all Altcoins and always keep better than that, because every investment is purely from the heart and is voluntary according to what we have personally analyzed.
I think he's talking about the danger from market cap perspective which makes sense considering the liqudity is lower than btc which means more vulnerable to manipulation but I do agree.
None of investment instrument that has zero risk and the profit usually as big as the risk it's just the law.
Even stock market right now could crash as hard as btc back then. The crazy volatility not only happening in crypto market.