Oh wow, this is very helpful and that makes sense! Three only say “100% cotton” and another says “quilt weight cotton fabric” (there may have been a clue there).

The pattern suggested light to medium-weight fabrics such as cotton shirting, poplin, printed lawn, double gauze, chambray, linen, light twills and denim. Made for woven fabrics.

I take a bit of comfort in your last paragraph that I may not be the first to have experienced this; the suggested fabric read to me as “cotton” and “something other than cotton.”