I'm baffled at this sort of nonsensical justification of course mistakes. I've seen another one earlier.
The word "paterfamilias" was unequivocally taught as "head of the house" in previous lessons. Regardless of whether the original word can be embedded into English (which I've never seen in my life), why not stay consistent?
This is absolutely absurd. I don't expect the content to be perfect, but why not acknowledge the couple small mistakes it contains?
It's English, but it's also a loanword (obviously). We don't have our own word because we don't normally have the concept either. At least as far back as Saxon times, once a child reached the age of majority they were (legally) on their own. This is in contrast to Rome, where you were always subject to your eldest paternal grandfather.