The street level values returned by the geocoding service are broken down into the smallest level elements and returned in separate fields so the street type, "straat", is returned as part of a separate field named "StType". You can choose to also return "StType" as another output but another option is to request "StAddr" which will contain the entire formatted string of all street components as well as the house number ("Bosstraat 166" in your case).
If you need the street components without the house number, you could always post-process the "StAddr" to remove the value returned from "AddNum" from it.
Brad
