I don't think that you understood their answer correctly.
They didn't claim that tether is a potential scam, but that other stablecoins other than USDT/USDC/DAI are scams/potential scams, and they don't wanna support whole other network (Tron for example) just for 1 stablecoin. (in this case USDT).
I think he understood it correctly. The reply suggests that Tether is a risky coin and/or a potential scam, and that's a completely valid concern. Everything about Tether is shady, and while people have been saying that it would burst soon, it somehow managed to survive for years. Still, that doesn't make it any less risky, so not wanting to support a whole new network for a risky coin like USDT is, IMO, good reasoning.
The other question we should ask is, how many people use Tether and care about privacy? Will having USDT on TRX20 eXch be of any real value? I doubt it.