When you create a survey, you have the possibilities to make all the feature layers private, so that the survey can be public, but the only thing submitters can do is submit. 
However, on the details page (above) of the open feature layer for submission, one can still access the URL of the services (below), meaning that anyone can see the survey questions. 
Idea: I would love to see a feature where no one can see anything except the survey and only if they have the link to the survey. Completely controlled by that https://arcg.is/xyzexample link. Dreamy.
