Sounds extremely familiar, I am partially face-blind, so I have had plenty of those encounters, over the years. So far my worst one was, when I completely forgot a teacher, that was teaching the art class I was taking, for a year. I had zero recognition, even after they told who they were - and they remembered me very well. Talk about awkward... I just do not learn faces, and if I learn to remember them over long, continuous exposure, I will quickly forget again, once we stop seeing. I cannot even form a full picture of a face in my mind.