It looks like you're decreasing on that row.
Are you confused by the numbers in parentheses? That's generally "for medium (large, extra-large)". In other words, "rib five (for large, rib one, for extra-large, rib five) rib 2 together, then rib so many (for large, eight, for extra-large, eight)..."
It helps if you go through the pattern with a highlighter and highlight the instructions that go with the size you're making. In general, a number after a row means "you now have (this many) stitches", which is handy if you've increased or decreased or if you're working in lace where the rows have varying stitch counts because of the pattern.