As sickening trivial as this is compared to the tragic occurrence which created this argument, mildly interesting in a consideration of ethical language use.
The term "female" is - on its own - a descriptor; it described a detail about the subject. It is fair and accurate, just as it would be to have titled the thread "middle-aged cyclist..." or "Mancunian cyclist...". You could quantify it as sexist through precedence. If the originator of the statement had started many similar topics before and had always habitually omitted descriptors for male subjects you could argue that it was sexist on the basis of needless gender definition, but that to my mind would be tenuous at best and I don't believe such precedence exists. If there was any implication that the female part of the sentence had any bearing on the outcome, that could be hypothetically sexist (for example, "yet another female cyclist down") as there is then wiggle room for implied causation based on gender. If the thread opened up into a discussion on female cyclists being more, I don't know, prone to accidents, that's sexist. I didn't see any of that.
Simply pointing out that a cyclist down is of female gender I don't think reflects anything like sexism; unintended, unknowing, latent or otherwise. Its a needless detail at worst.
Someone argued somewhere in this thread that because someone had taken exception to the inclusion of the descriptor "female" it made the statement sexist regardless of the original intent. I'd say thats bulhooey, just because someone perceives that a discrimination has taken place, (a perception they are free to form) it doesn't make it automatically so. Perceptions can be wrong.
Just my own thoughts.