According to Eliza, how did she learn good manners? How is this an insult to Higgins? (Act 5)

According to Eliza, Pickering taught her manners.

LIZA. It’s not because you paid for my dresses. I know you are generous to everybody with money. But it was from you that I learnt really nice manners; and that is what makes one a lady, isn’t it? You see it was so very difficult for me with the example of Professor Higgins always before me. I was brought up to be just like him, unable to control myself, and using bad language on the slightest provocation. And I should never have known that ladies and gentlemen didn’t behave like that if you hadn’t been there.

This is insulting to Higgins because Eliza states she couldn't have been a lady without Piickering's example because she was brought up to be just like Higgins.