The reason why a drawing template opens with an associated sheet size is the way the template is saved. If I recall, the Tutorial template is setup this way.
The way to fix it is open the drawing as a new document but do not place any views.
In the feature tree delete the "Sheet Format". You then get a blank page
Then do a File > Save As > Template and overwrite the one you have
the next time you start a new drawing the prompt to select a sheet size will appear again.