Nobody, not even the ATF, is claiming he bought the guns illegally. They're claiming he was illegally "engaged in the business of" dealing weapons because he didn't have an federal firearms license. Prior to 2022 he wouldn't even be on the ATF's radar but "with the principal objective of livelihood and profit" was amended to remove "livelihood."

This is the form you fill out when you purchase a gun[0]. Please let me know where on this form you "promise not to resell" a firearm you purchase.

Straw purchases are illegal. Reselling firearms is not.

[0] https://www.atf.gov/firearms/docs/4473-part-1-firearms-trans...