Bearisgray provided the link to the words of Robert Kaufman on this subject. Unless I'm misunderstanding what I read, yes, if a product at Joann's or anywhere else is marked "Kaufman" and "Kona" it is the same product. They want to know if you bought their product and are not happy with it.
The only concern would be if you were not shopping carefully and you mistakenly bought a product that you thought was Kona but it was not that brand. Sometimes they're mixed up on the shelf, maybe other customers pulled one and put it back wrong. Your receipt from Jo-ann's (at least where I live) is very detailed about what fabric you bought, and it's all scanned electronically off the bolt, so not really subject to an input error on the part of the staff.
I found out just how great these receipts were recently when I got the last bit of a clearance fabric I loved for backing on a particular project and then didn't have enough of it when my quilt needed to grow. I called another Joann's about 10 miles away and they were able to track down the exact fabric from the information on my receipt and they had it and held it for me.