I think they might be talking about the strip method. You take a few selvage to selvage pieces in the height you're looking for (2.5 inches are the jelly roll size) and carefully sew three rows together of each set. Double check that you're consistent during this part or the whole thing will be off.
You then cut off sections the same width of the sewn rows as you're doing height of the individual pieces and combine your sections to form nine patches. there should be info online for "strip piecing" if this is the method you're looking for.
Happy sewing!