It contains all the measures in your data, collected into a single field with continuous values - This is the definition for 'Measure Values'.
All others are True w.r.t. Measure Names!
The Measure Names field contains the names of all measures in your data, collected into a single field with discrete values.

Documentation : https://help.tableau.com/current/pro/desktop/en-us/datafields_understanddatawindow_meavalues.htm