The market has realized most of these coins are worth nothing and some promoters have no intention of developing the ecosystem
Not all altcoins are worth zero. The altcoin such as Ethereum, Cardano, XRP, Binance Coin, Litecoin, .... will have high value in the future when the market gradually recovers.
The guy meant those tokens that take 300+ places in rating. many of them were created to be pumped to dump them after. Yes, they can cost zero after it, and you need to be very cautious when you decide to buy them.