Created two incidents for John Doe and went to create another incident and his name was auto-filled into the fields. Have found that this occurs with other fields on the form as well, from time to time.
This happens because "Enable smart fill on repetitive input of some values" is enabled on the Form View for the business object Layout. This is enabled by default, and when entering repetitive data, the system automatically enters data into certain fields (not template fields) so you don't have to type the same thing over and over. The user can overwrite the information if needed.
This generally stays active and will continue to fill until you logout and end the session.