caniplaywithmadness
No, a policeman does not have the power to demand for the sake of it. However, as you are well aware, you do not know the full circumstances of this incident. You were not on with the PC, when he made the requirement, nor are you party to the full details of what the woman said, or did not say.
Without those bits of information you are not able to say the officers had no grounds for requiring a test.
It's always easy to be critical when the full facts are not known, or rumour is listened too.
Like you, all police officers have been there seen it and done it. I can also presume you, like me have also bent the rules slightly to do people a favour and show someone accusing them that there is no substance to what they think. Thereby saving them from making allagations later when what they say cannot be disproved.
Whatever Police do it will upset someone. Most officers accept that as a fact of life.