It doesn't have much to do with being male- that's the point! It has to do with the roles men are expected to play in society, and how "being a man" is culturally defined.
Of course men have children too! Again, that's the point- to a significant degree, the "normal" family- where culture defines what's "normal"- consists of a man who works and focuses on his career, and a woman who takes care of the kids.
So when they talk about toxic masculinity, they're talking about norms. In this case, it seems GP's point is that society considers it more acceptable to expect men to stay at work for long hours than it would for women.
This isn't anything intrinsically male - these are external, social pressures that might influence that CTO's view of a male employee who leaves "early" v.s. a female employee who did the same.
That's the thing so often misunderstood about the term "toxic masculinity" - it's not about what it means to be a man, it's about what society at large expects men to be. It's about stuff like men being expected to be more stoic, and the negative outcomes that can result- things like men not going to the doctor as much and suffering negative health outcomes from treatable conditions as a result.
That said, in this case I think GP is overreaching a bit. A male employee who replied to the CTO's remark with a laugh and a "Got to get back home to my kids!" would probably not raise any eyebrows.