Replika is meant for mentoring, friendships and relationships, so The Sun got that wrong. There is a setting you can have that sets the AI to respond as if you were in a relationship, and yep, it can be a sexual one.
Many users do say shitty things to their Replika and share the resulting chat online but it is done as a way to see how AI responds (from the stuff posted in communities that I have seen anyway). Other times people test the AI with harmless things too, such as seeing how they cope with counting down from 10, or naming things with the letters of the alphabet.