The quest refers to the crosswalk path itself, thus generating on the path itself.  In this case, "no curb" should be selected in StreetComplete.

It also asks where the crosswalk meets the sidewalk/footpath.  This one is different since it is on the nodes, and the quest is for that specific node on the path.

I know, StreetComplete can be weird with quest placement.  Feel free to reach out if you have any questions. 