It is a trend or fad.
No different than being a “valley girl” or a hundred other fads.
Just this one comes from the sexualization of youth, no different than being trans is often a fad rather than real body dysmorphia.
Except this fad can kill.
You’re right. They are identifying as bisexual, but still only have sex with men.
Here is an article with statistics showing that -
https://quillette.com/2022/06/14/progressivism-sexuality-and-mental-illness/
“Dysmorphia” is a deadly fad as children and teenagers re pushed into transing and very high suicide rates. it is a facet of social suicide as evermore are rendered unable to produce children and the birth rate declines rapidly.