Making a Loose Chair Cover

I tried to understand these instructions but they just don't make sense to me. I understand the cutting instructions although I'm not convinced they are correct.
Then step 4 in the sewing instructions ask me to sew around the three sides but to leave the front arm edges open. If I do that how are there 3 sides to sew?
Can someone clarify this for me?

Hi there,
Thanks for your query. We're going to check this out for you and get back to you as soon as we can.
Thanks
The UKTV Style Team