I think what you were trying to say in your original comment was that "positive" sexism doesn't exist. That the author was being unreasonable when she interpreted her co-worker standing up for her as sexism.

I will assert that such "positive" acts can be and often are sexist. Negative actions can also be sexist. It is possible to take a sexist action while you think you're being helpful. Not all sexism is manifested in malice.

Consider similar racial stereotypes like "Asians are good at math" or "black people are good at sports." You might think that someone is positive, but those beliefs are deeply rooted in racism and racial stereotypes.