Hello Nel,
It is a bummer isn't it? The first time is the most difficult, but the memory comes and goes in cycles so, on another day, he may say hello and know you perfectly well.
Saying "who are you?" may in fact mean "I know your face but I can't remember your name". He may just be having a bad day.
You did exactly the right thing in continuing as if things were normal. That is such a major lesson, but it hurts, doesn't it? It'll hurt less as time goes by, but do keep on. If this is the first time it has happened, then he may know you next time you visit. It may not happen again for ages, or it may be the same next time. There's no way of knowing.
I always start a visit with my wife by saying "Its your Bruce, come to see you". I always hope that something of that registers with her.
When the situation got this far for my Jan, I found that it helped to start a new kind of relationship with her, based of course on the past, but setting new standards for contact and communication - and expectations. It was less hurtful that way.
Of course the memories are there, for you or me, at least.
However, the little familiarities that everyone has with family or husband/wife - those may have gone, at least for today. There will probably be at the very least, flashes of them as you visit him in future. They will be worth waiting for, believe me!
Once my GP told me that my wife was still Jan, and that I simply had to dig a bit to find her. I didn't believe that was true at the time, but he was correct. My wife can't see, she can't talk most of the time [and can never make sense when she does], she can't walk, can barely crawl, and I'm sure she doesn't know me - but she is still Jan, and even at this late stage, I still get glimpses of her old self.
It is worth the wait.
Do use Talking Point whenever you feel the need. It will not only help you, it will help others, too - including me!