You are correct, this is only for models with the cellular option. Wifi-only models can skip this step.

This did not work for me. Finally I just pulled the two parts apart at the bottom side, carefully twisting and manipulating until the parts clicked loose at the top side

If you are comfortable with repairs and are carefull during the procedure, you don’t need to disconnect the display. Use an elastic band to hold it straight against a box, see last picture in step 14, it saves some time. I managed to do it in 45 minutes.