Yup, I'll admit I'm a moron. I'm still thinking about Charlie Morton as an Astro and I was thinking he was supposed to be on the AL League Leader card and he's actually on the NL League Leader card because, well the Braves are in the NL! Dummy me.
Anyways, I see it is probably not an error on his card even though he did not lead (or tie) the league in any of the categories listed on the back of his card, but rather the line is unnecessary. Topps typically only adds that line for those that actually did lead or tie their respective league in a statistical category listed on the back of the card.
However, it appears that ALL of the league leader cards in 2022 Topps Series 1 have 'AVG' on the back of the card instead of the category for which they are listed (Wins, ERA, HR, RBI, Strikeouts) and it would appear that 10 of the 12 cards should be listed as UER.