No, boys were almost certainly not so forbidden.
See, dress codes, particularly in today's day and age were and still are generally vulnerable to a specific challenge on the grounds that they discriminate on the basis of sex.
You are being obtuse if you say that school administration is blind to that fact. In fact, they are the most poignantly aware of such challenges because kids are clever, rules-defying bastards, and will look for almost any opportunity to subvert the intent of a rule. This is almost certainly why they went with a "gender neutral" dress code: to kick and scream rather than be dragged into the 21st century. They thought they could "avoid a controversy" and put a fig leaf over what we can all agree is a bad policy that is pretty transparently an attempt to prevent discussion or acquiescence on some absolutely fucking pointless thing that for some reason school administrations think is the most important thing in the world; whether that issue is girls wearing short skirts ("Slut! Harlot! LET'S BAN SEXUAL EXPRESSION, because NOT TALKING ABOUT IT will make it all go away, right?"), Or boys wearing skirts ("OH, THE SCANDAL!"), Or trans-girls wearing skirts ("ThEyRe ToO YouNg To thINk aBoUt PuBeRtY" -- even though they're being forced to go through a puberty they would rather not have), or even trans-boys NOT wanting to wear skirts.
All the usual suspects for administration motivations could be in play here, but none of them, except for cis-boys and trans-boys get any sort of "what they want", and even then, it's an insult to their freedom to choose.
Edit: Hell, 2-3 years back, give or take a year, I recall a rash of stories about boys at uniformed schools wearing skirts, of girls wearing pants, as either solidarity to trans schoolmates or in protest of gender discrimination on dress code, and resulting challenges to either the lack of explicitly naming gender restrictions or to exacerbate admins over the failure, and the resulting discussion of whether it was valid in the first place to pin them to gender given non-discrimination laws.
You may have a short memory, or low exposure to the issue. School administration officials and boards, however, would not be. They would have specific visibility and long memory of the incidents, and possibly many more incidents that never saw media coverage.