Sure, if you zone in on the prefix, it definitely means two, but the word bisexual itself has been used to denote "attraction to more than one gender" for ages.

Do not assume that bisexuality is binary or duogamous in nature: that we have "two" sides or that we must be involved simultaneously with both genders to be fulfilled human beings. In fact, don't assume that there are only two genders.

–Excerpt from the first edition of Anything That Moves, a bisexual magazine, initially published in 1991