Did you miss the part about it being about choice?
Did the man at the door force her to accept his invitation?
If not, this is not sexism. This is someone extending an invitation. If you would like to metaphorically, “Close the door” on such invitations, you may find yourself rather isolated. Then again, perhaps that is your preference. If so, simply tell them, “No, thank you.” Why is that so such an imposition on social interactions?