I thought the whole routine was pretty bland and nowhere near Ola's usual standard of choreography; apart from the cape twirling, it was difficult at times to tell whether they were attempting a paso or a tango.
Maybe Ola realised this and thought the crotch clutching would liven it up? If Robbie had done it once he would have got away with it, but 3 times in one routine was too much; and right into someone's face (never mind who that someone was) was the height of poor taste at best.
Although I agree the pros set up the choreography, the celebs can refuse to do a move they find distasteful, so both Ola & Robbie have to take responsibility.