It seems she, being his direct manager, was a large part of the reason he decided to leave after 18 years. There is probably a lot of anger and frustration. I do agree this part of the post could have been phrased better.
It's Ian Hickson - the co-creator and lead of the entire Flutter project. He described her in his post as "Jeanine Banks, who manages the department that somewhat arbitrarily contains (among other things) Flutter, Dart, Go, and Firebase". As the head of Flutter he would be directly underneath her in the corporate hierarchy.