Trans men get periods?
While it varies widely, it commonly takes several months on testosterone to stop menstruation and not all trans men take T. It's usually years on T before a hysterectomy would be a recommended option. I personally don't know any who would be 'offended' by the content though I know some who would avoid the content when their dysphoria is really bad.
I've seen content warnings for food, alcohol or drunkenness or drugs, diets, medical procedures, certain animals like spiders or snakes, mentions or images of blood or vomiting...while I agree it's a bit weird coming from a company selling menstruation products and I strongly disagree with menstruators and 'people with X' thing and don't think it really helps anyone but those that want to appear progressive, content warnings aren't about something being offensive and the concept of triggered - which has been entirely fucked up in popular culture - is not meant to be a value judgement though it certainly has become that way and I know there is a lot that has been said and written about the issues with content warnings as they are now used. It's meant to be about knowing your audience and letting them decide if they want to read something. If your audience has a significant number of people with dysphoria, that sort of content warning makes sense.
I once went into a panic attack and sobbing mess by hearing someone else be asked what they as a child had wanted to be when they grew up. There is obviously nothing offensive about that question, that didn't stop me being triggered because being triggered has absolutely nothing to do with being offended. Yeah, my feelings are fragile at times and I fully admit it, but I can't really think of another term for those who think that writing a content warning makes a person a horrific evil.