Bisexuality literally means two genders that someone can be attracted to. I suppose what they’re saying is they’re attracted to two genders and non-binary takes up one of them.
“Bisexuality is romantic attraction, sexual attraction, or sexual behavior toward both males and females, or to more than one sex or gender”
I think this is where people start to get confused, saying bisexuality = male and female. Traditionally, yes, most people who are bisexual only are attracted to male and female. But bisexuality literally means attraction to two genders. So that could mean non-binary and females, male or female, or whatever combination of two genders there are. Pansexuality - pan meaning all - literally means attraction to all regardless of gender or someone who’s attracted to more than two genders. So yes, a bisexual indvidual could be attracted to transgender people, depending on their outlook. They can be attracted to them because they find them male/female regardless or they couldn’t be attracted to them because they’re attracted to cisgendered males or females. Bisexuality on it’s own is a complex and slightly controversial topic though and this is my outlook on it.