I think he meant the most famous stablecoin out there. There's no doubt about it since the majority of Bitcoin trades are traded in USDT, it even outshines altcoin trades.
Anyway, it's not like it's the end of Bitcoin when people suddenly lose trust on USDT. By far USDT is probably the most suspicious stablecoins out there because of lack of audits and reports on their assets so other predators (other famous stablecoins) will likely try to market their coins to replace the spot of USDT.
I don't think there's going to be any big problem since people have a lot of choices to make. Either use another stablecoin, withdraw their money from exchanges, or use altcoins just like the old days. Sure there's going to be FUD happening that will affect all cryptocurrency (since almost every altcoin is using USDT for trades) but that's only temporary.
Even with that in mind, it would not make any sense that crypto would fall, how could it fall? I mean shouldn't the idea be that people would want to sell their tether and get crypto instead? Shouldn't that cause the price to go up? I mean there is really no logic here where tether being worthless could hurt crypto, after all people who run away from crypto should be capable of actually increasing the value of bitcoin instead, that should be the case honestly.
Of course this doesn't mean that tether will suddenly go down soon, or it doesn't mean that people will lose hope right now, I just mean to say dude said crypto could be bought cheaper because most crypto would be pegged to USDT but I feel like just the opposite is more possible. In fact it would be great for bitcoin if USDT turns out to be something bad, at least people who hold USDT would exchange it for bitcoin no matter what the bitcoin price would be.