Looking at the pattern, it calls for fifteen 8.5" squares to be cut out of each of the 6 fabrics. If your fabric is very wide you might be able to get 5 squares in each width of fabric, but this would require 42.5" of usable width. Most fabrics don't support that. But if that was the case, you could get by with only 25.5" of fabric for the 15 squares.
Most fabric will provide no more than 40" of usable width, so it's more likely that someone would be able to get only 4 squares in one WOF, meaning that they would need another 8.5" in length, or 34". If you actually need 34" of fabric, you may not be able to get it from one yard, given that you may want to pre-wash your fabric (and it could shrink) or your fabric may not be cut straight when you buy it. The pattern maker has to take these things into account when figuring yardage.
So - I side with the pattern writer on this one.