I've never felt the need to introduce myself to anyone as "I'm Chewbacca, I'm a nurse (or whatever) and I'm heterosexual". Why is it now so important to label ourselves regarding our sexuality? Does anyone really care what someone else does, provided it doesn't harm anyone else?
Most of us don't have to declare anything, but as a journalist was about to run a story about her being in relationship with a woman, and maybe had evidence of other relationships of different 'types', maybe LM felt pressured into making some sort of statement.
Personally, I couldn't care less, but it is clear from some of the 'jokes' on this thread that a lot of people feel the need to comment on the labels, so maybe it makes sense to get in first.
Also, during the election campaign, Jo Swinson had very definite ideas about the Gender Recognition Act, so maybe it is deliberate LibDem policy to be inclusive?