"He calls his wife."
Translation:Il appelle sa femme.
"Femme" would be a weird name, I think.
"il s'appelle Femme" would be "he is called Femme".
So, to name someone, you would use verb "appeler" in the pronominal form.
That pronominal form can also be used for reciprocal/mutual calling: "ils s'appellent de temps en temps" means "they call each other from time to time".
Yes, Duo should apologize, for this error was reported months ago and their devs have been too busy to amend the system and prompt a correct warning.
The issue is that "son épouse" is obviously not masculine ("son époux" is masculine), but it uses the masculine version of "sa" for euphony reasons.
[sa épouse] has a vowel sound conflict that has been fixed by using the masculine "son" instead.