From a Judge. The statement means that any long seam - be it sashing or just straight line of blocks sewedtohether should be straight. Pictures might not show correctly but it appears that the 4th row from the bottom, the one long in the center just at the top of the white card on the right bows a bit and does not appear straight.
Now before anyone says - "it looks ok to me" or "what are the judges talking about", remember that the quilt is in competition with others and if one quilt has all long lines of sewing that are straight and one is not,......then which one gets the ribbon.....If you had a company put new tile on the kitchen floor - would you want them straight or some slightly bowed.......same in quilting.