The phrasing "majority of all cases, especially in the developing world" implies that it's true everywhere. Even putting that aside, it's only the bizarre situation in Africa makes the statement technically true. If we interpret it in the way it was meant to be interpreted then the statement isn't really true because everywhere that has reliable data shows the opposite: men get it the most.
I don't think the 'especially' has that implication when you consider the context of the article that we're commenting on. It's true that women and girls make up the majority of people living with HIV worldwide, and this is especially true of the developing world. On the other hand, your statement that "the vast majority of all cases are in men" is simply false. Depending on the interpretation of 'vast', it's arguably not even true in much of the West. For example, in the UK, about a third of people living with HIV are women; in the US it's about a quarter.
There's nothing 'bizarre' about the situation in Africa. People's sexual behaviour is different in different societies, and this can obviously influence how STIs are distributed among different groups in the population.