If we are talking about whether or not sexism occurred, then it does not in fact matter what someone said before or after they said something sexist.
It does not matter with regard to the assessment of his remarks as sexist, but it does matter with regard to his perceived attitude towards women and how that perception will impact his reputation. The author was right to call this guy out for his sexist comments, but it was not right for him to omit 50% of the transcript that shows this guy is actually a human being and not the paragon of male sexism and misogyny.