At this time "house dress" has a slightly different sense than it will later. A dress with a Watteau back and the option for a train isn't designed for scrubbing floors. Rather, this is a dress worn at home. This distinguishes it from the various types of dress worn outside the home such as tailor-mades, reception dresses, evening dresses, etc.
I think the house dress could be worn when informally entertaining close friends; lemonade and gingersnaps on the porch, for example. In this regard, it's not unlike the tea gowns just coming into fashion.