Happy Egg Co uses 4 breeds of chicken -
Since my package had only brown eggs, that rules out the Legbar. Are any of the other 3 breeds a sex-link breed?
Lohman Brown and Hy-Line Brown would be sexlinks.
Black Copper Marans are not sexlinks. (And that's what their "Copper Marans" are are, according to this page: https://happyegg.com/happy-birds/)
Of course, if they run all the breeds together, then an "oops" rooster of another kind could mate with the sexlinks too.