it really isn't. nonbinary people have been calling themselves lesbians, which absolutely does contradict the definition of lesbian. lesbians are supposed to be females that are attracted only to females, and when a nonbinary person calls themself a lesbian, they're misgendering themself. most enby lesbians only identify that way because practically nobody has ever heard of the label that is specifically for enby lesbians, trixic.
a lot of women don't like that the definition for lesbian has essentially been changed to be non-men attracted to non-men, so instead of trying to fight back, they made a new label for themselves.
please note that i myself am nonbinary, so this is not from a biased source.