The list you see under Manage Columns lists all the fields on your form. They are named based on the Title property and ordered by their appearance on the form. It is important to note that in the current version, not all listed fields can actually appear on the report. Only input elements will actually display on the report because only they store data that can be displayed. Input elements include Single Line Text, Multiple Choice and Checkboxes. Unsupported elements include Section Breaks, Text Blocks and Collection Tables. Some unsupported elements will appear in the report if selected, but won't display any data. Others will not appear on the report at all.
This topic will be updated as the Response Form is updated and improved.