She's not self-shading, she's pointing out how funny it is for BTW to be called a flop when there's a sold out 55k stadium in front of her paying to hear it.
She is obviously being sarcastic. It is like she is saying to all the haters, "**** you if my last album was such a flop, why am I selling out Twickenham?".
Although it does seem like the joke went over the audience slightly.