Oh, boys can absolutely have image problems for looking at instagram models. In general, comparing oneself to the photoshopped version of people that are already in the top percentage in the good looks lottery is bad, regardless of gender.

However, statistically speaking, boys just don't follow male instagram models in the first place. Far fewer install instagram in the first place, and if they do, it's not to get fashion tips and lifestyle advice models. Those that do are probably going to end up very insecure too. But in practice, boys don't do that, and therefore the practical levels of harm are lower. It's just like how teenagers that have friends that binge drink end up having more alcohol related problems. It's not that the alcohol itself is more dangerous, physically speaking, the more friends that drink the teenager has. It's that if their friends are binge drinkers, chances are higher that they themselves will binge drink too.

Also I don't think it's 'kosher' amongst the male species to admit and seek mental health assistance either – so THAT correlation could be an important one.