"Bisexual" girls categories
2. confused lesbian
3. confused straight girl
4. straight girl with a very high sex drive
Many lesbians have identified as bisexual at one point. Even YouTuber, Ariel Scarcella, admits that she has misidentified herself as a bisexual even though she's a full lesbian. Internalized homophobia would also provoke someone to identify as half straight.
It's very common, especially for teenagers, to be confused about who they are. There's a study that proved that lesbian women and straight men are only turned on by women and their attraction to females increase as their sex drive increases. Straight women, on the other hand, are typically aroused on by a wide range of sexual stimuli (including animals too), but are only capable of feeling attracted to a man. Straight women with higher sex drives get aroused more by every sexual thing that happens which may lead one to believe that she's bisexual even though she's just a straight women who's a sex addict or a pervert.
"Bisexual" guys categories
2. confused gay guy
3. confused straight guy
4. straight guy who's a sex addict and will fuck anything that moves because of his high sex drive
Again, it's very common, especially for teenagers, to be confused about who they are. Many "bisexuals" are going through a "bisexual" phase right now. And many former "bisexuals" have gone through this phase as well. It's quite ironic to see that if a gay guy says he's slept with a woman before and claims to be fully gay, no one will challenge or deny that. If that's possible, I'm sure it's still possible for a straight guy to sleep with a man and still be only attracted to females. There are confused straight guys as well as confused gay guys. Many people don't understand what sexual orientation is because they confuse behavior and arousal for attraction.
There was a study that examined the arousal patterns of "bisexual" guys. Some of them didn't experience any arousal during the study. Many of them were only aroused by gay porn. One of them was only aroused by lesbian porn.
Mice are mammals as well and many psychological studies are based on the study of mice behavior in order to relate with human behavior. Male mice with high sex drives didn't discriminate between which gender they wanted to sexually hump. It's not known whether or not the male mice with high sex drives are actually turned on by both genders. My guess is that, just like straight human males, the male mice are more turned on by the opposite gender as their sex drives increase, but in order to relieve their high sex drive, they will fuck anything that moves when there are no readily available females. It's very common for straight guys to fuck objects, experience paraphilia, and/or basically fuck anything that moves when their sex drive is way higher than the average male's sex drive. If they don't resort to that kind of behavior, they will resort to other destructive behaviors. What you do and what you are turned on by are two different things. Your behavior doesn't determine what your sexual orientation is; your genuine, PRIMARY attraction to a gender does.
Lippa, R. A. (2006). Is high sex drive associated with increased sexual attraction to both sexes? Psychological Science, 17, 46-52.
Study: Bisexual Men Not Aroused By Both Sexes, page 2, by Daniel DeNoon, wedMD.