Question on "out of wedlock" notes in census

I am trying to figure out why my ancestor is listed - along with some siblings - as born out of wedlock when their parents were shown as married in an earlier census. Eivind Wilhelm Johannessen, who came into America about 1893 as Evend Haugjas from Canada. Have not been able to locate his departure from Norway either. Any assistance would be appreciated. 1875 Census http://digitalarkivet.uib.no/cgi-win/WebCens.exe?slag=visbase&sidenr=2&filnamn=f71301&gardpostnr=464&merk=464#ovre