I got a feeling of incredulity from reading this article because it seems like the article is saying that sexual fluidity is a sexual orientation, you can be asexual, gay, straight, bi or fluid. But that seems like falling into the same type of rigid thinking that the article decries. I think sexual fluidity is orthogonal to sexual orientation. If right now you're attracted to both men and women, you're bisexual. If, in a few years, you find yourself attracted only to men (as a man), then you'll be gay.

I think the problem arises because most people consider sexual orientation to be an identity, instead of a description. Some languages have multiple verbs that are covered in English by 'to be'. In Spanish, for example, there's ser and estar. Ser is used for things like inherent characteristics, while estar is used for temporary conditions, moods, etc. If you say "I'm tall" you would use ser, if you said "I'm tired", you'd use estar. People tend to think of sexual orientation in the ser sense instead of considering that it can be used in the estar sense.