I think that Miss Bates and her friendly chatterers were chattering about Emma and Mr. Elton. Mr. Elton is a great friend of Mr. Cole's, and they probably talked about it--at least a little. After all, Mr. Cole wasn't shy about hinting to Mr. Knightley about Jane Fairfax. From Mr. Cole to Mrs. Cole to Miss Bates--with several others a part of the chain, no doubt. I think Emma is more likely--and all the more reason for Mr. Elton to dislike her immensely.