As far as I am aware (DS plays rugby) handing-off is meant to be done to the chest or shoulder, and refs will blow for a penalty if it's done to the face. So it sounds like the person making the complaint committed a foul, and a potentially fairly dangerous one at that, which left their opponent bleeding. That's not to condone the opponent retaliating, and spitting blood in someone's face is unacceptable.
But I do wonder whether the RFL needs to look again at what stage people need to move from the women's to the men's game if they're taking testosterone.
And I would strongly argue that it is unsafe to let transitioning people going the other way, i.e. biologically male individuals transitioning to transwomen, ever play a contact sport like rugby. I cannot see that there could ever be any justification for letting biologically male individuals play against women in a high impact contact sport which already carries an exceptionally high risk of concussion and spinal injury.