Yeah, usually if it's supposed to be provisional, they will say so. It may also be a mistake that they said to use kitchener in the pattern.
You know, you probably don't have
to use mattress stitch. I just think it makes the end product look tidier, but you could probably use whatever seaming method you want, as there aren't that many stitches to seam.
There's a great article on Knitty about seaming that you might want to take a look at: