This happens because the Students Name does not match. This could be there is a different spelling in the last names, first name, or a nickname. The candidates name must match exactly in order for it to display the Dropdown for Inquiry Years in the Users record otherwise this will create a new User.

On Step 3 of the Create a Inquiry it will say New User or show the existing 
user. If you do not see Show the Existing User then you must have a spelling error in the name which means the users do not match.