USDG's peg depends on reserve backing, issuance/redemption and market arbitrage.
When eligible market participants can acquire or redeem tokens near one dollar, a market-price deviation can create an incentive to buy or sell USDG until the difference narrows.
Secondary-market liquidity is also important. If exchange or DeFi liquidity is thin, a trade can deviate from one dollar even though the issuer's redemption framework continues to target parity.
The correct interpretation is therefore "designed and redeemable around 1:1 under the issuer framework," not "every market trade must always execute at exactly $1."