I think what happened is that you may not have had a good , at least 1/4 inch seam allowance and the quilt appears to be tied. Looks like it was not tied close enough and when the washing machine agitated the fabrics pulled more since the tying was so far apart. When you read on the batting packages how far apart the quilting needs to be, at a minimum, I think same might apply for the tying. Too much pulling on the fabrics during the washing process.