The thread you linked to claims "i’m sick of every post i come across being about sucking dick and ‘girlcock’."
I have reddit and ran a search for "girlcock" on r/actuallesbians and there's two results from 4 and 5 years ago.
Scrolling through the posts on r/actuallesbians I don't see anything about "girlcocks" or trans people.
I suspect someone is having a slow day and is lying to cause trouble.