LUNA – a native token of Terra – had the 8th largest market capitalization among cryptocurrencies with nearly 40 billion USD in April 2022. The role of LUNA is to maintain the value of TerraUSD (UST), which is a stablecoin pegged to the US dollar in the Terra ecosystem. Unlike other well-known stablecoins, such as USDC and USDT, whose stability is secured with reserves of assets, a dollar peg of UST solely relies on the use of LUNA.
You friend is only trying to warn you about other stable coin not to crash just as Luna crashed, the quote above is just a snippet of what LUNA is and it's stable coin TerraUSD but you can read the full details on the topic
Dissecting the Terra-LUNA crash: Evidence from the spillover effect and information flowThis article provided will help you get an information of what happened to Luna.