This is false and unfortunately spreading like wildfire, UST is not collateralized by Luna. Ultimately I am very bullish on decentralized stablecoins, Dai also had many issues early on, this is but a rite of passage.
The Terra UST stablecoin could collapse in a bank run effect. UST is backed by an endogenous collateral Luna. Current Luna marketcap has fallen to arguably < outstanding UST. We are now in a dangerous spiral: as users panic out of UST, this reinforces the Luna crash further.