So this is weird. My 1949 book has Rock as coat and Mantel as overcoat. Duolingo and other places teach Rock as skirt and Mantel as coat. Is the book just wrong or a long time ago was it different?
I just looked up in the glossary in the back and it has Rock as coat and skirt.
only that Rock as in surcoat is mostly out of use nowadays. That leaves younger folks baffled when they hear old sayings like "das Hemd ist mir näher als der Rock". That only makes sense when Rock is used as Gehrock and totally incomprehensible when Rock is a skirt
The book was done in the late 40s so that is the time frame of when they said Rock was coat.
You can still refer to a coat as a Rock, but these days it mostly refers to a kind of old fashioned clothing. It's not like the clothes themselves have changed so much, but if I would hear Rock (or Gehrock) today I'd think your describing a picture of the 17th or so century to me, not the clothes I'm wearing to day.