Family relationships in census

Re: 1865 census for Nes, Head of household Hans Thores. (person #4031) and family on Ertserud Sæter Maalerud farm. Hans is listed as being widowed, yet Thorval and Gulbrand are listed as his sons (makes sense) while Marthea, Martin, and Ole are listed as their sons and daughter. Who is the "their"? Just a mistake on the census taker's behalf? Son Martin is my great grandfather, so I'm curious.