No I do not think that sexism doesn't affect men. Pretty much not a single person in the entire world thinks this. Longer jail sentences for the same crime is a classic example of this in action. How men who are victims of domestic abuse are treated by people is another one. You and any of the people that talked to you about that stuff are doing it wrong if they are applying anything at an individual level. What is actually happening is on the population level. On average men are trusted / respected more than women are. This doesn't invalidate your experiences. Anyone trying to do that is flat out wrong.
I'd say that men are trusted and respected more than women when it comes to their ability to act on their own, but certainly not when they express that they need help or are in danger or pain. Women's agency is certainly generally less respected, but so is men's vulnerability. That said, just because we know women's agency is sometimes disregarded doesn't mean that we can carelessly make examples out of situations that don't seem to show that pattern at all. Yes, people are more likely to fail to take women seriously. It does not follow that people only criticized him because they mistook him for a woman.
Actually that's not the case, women are often less trusted then men when they say they are feeling pain. Source