Yup, because fog is a relatively common thing, and “proper fog” (where you might be able to see the road in front of the car, most of the time) isn’t unheard of.
And yeah, in the UK it’s an offence (though you’re unlikely to have the police bother you unless they’re having a bad day) to drive with front or rear fog lights on when visibility isn’t low enough. Our front fogs won’t come on with other lights automatically though, for exactly that reason.