The comment on an email said that someone was "the husband to my mother". Would it not have been simpler to say, "your father"?
Not necessarily. I mean, yeah, my stepmother-in-law is the closest I'll get to a mother-in-law, but that doesn't make her into my spouse's mother.
Granted, FS does tend to gloss over such details in its fluff campaigns, but luckily, one can simply not subscribe to those.
In most cases - yes I would expect and have seen that FS obviously knows who "my father" is - and references him as such - sometimes in the automated notifications in ref to people in FamilyTree (which could be any relationship - sometimes we have seen weird things like this that you report)
if it was your Father - of course - it would have been better to simply ref him as your father. But not all spouses to a mother are the child's father - even though in your case - indeed it was kind of silly for the system to have worded it the way it did. . .
It is not uncommon for these automated notifications to go out with bad wording . . .