Sanekata held the office of Assistant Captain of the Middle Palace Guards 兵衛佐 from the 2nd day of the Second Month 978 until the 1st day of the Second Month 984, so the poem can be dated to some time during this period.
Given that unrelated noble men and women had very little contact, it was entirely possible for a man to visit a woman claiming to be someone else and leave her none the wiser as to his true identity.