I haven't seen this as an explanation for why someone would use bi lesbian as a label but here it is: they're abro (think of it like the genderfluid of sexualities) and fluid between bi and lesbian
oh idk if ive heard that term before ! i havent met anyone using bi lesbian like that yet, but its defintely valid owo !!
actually i just looked up the abro flag and ive seen it around but ig i never saw the term itself (or it didnt stick in my brain lol), its so pretty !