I can take a traditional pattern (one in public domain) and design a quilt setting using that pattern. I copyright MY instructions and MY setting and MY words. I do not have exclusive rights to the traditional public domain use of that particular block. I can only copyright MY version of that particular pattern. Personally, I always consider it a compliment if someone shows a quilt made from one of my designs. I do appreciate, if they use my pattern, to state that was where the design came from.
For over 40 years I have sketched blocks and settings on graph paper. I am sure that some are the same as others have done. In fact I have gone back in my sketch books and found the same block design, in a magazine or book. How many ways are there to draw lines on graph paper? If anyone else designs that way, why would they not have drawn the same lines?