I think it is worth looking at the Kinsey scale. See https://en.wikipedia.org/wiki/Kinsey_scale
When people’s actual attractions or behaviour varies like that, how do you map that down to the three labels in common use: straight, bi and gay? Do you call 0 straight, 6 gay and anything in between bi? That makes bi a pretty wide category and, if you hear that someone is bi, you expect that their attraction may be more nearly equal or that at least their attraction to both sexes would be enough that they would consider having a partner of either sex. So if you have bi as such a wide category, you are then looking for qualifying labels to say what kind of bi and bi-curious is presumably an attempt at that, though not a very good one.
Then you have someone at point 1 on the scale who may lead a straight lifestyle, get an opposite sex partner etc. but may do something occasionally with a same sex partner, or just sometimes has fantasies like that. Something that is low key enough that they don’t consider allowing everyone to think of them as straight as being a gross misrepresentation.
