What's to explain, we know that the dead do not come back to...

What's to explain, we know that the dead do not come back to physical life, so Christ may have appeared in spirit, the appearance may have been in the sense that the faith of those 500 souls was so strong that it was as if Christ stood before them in the flesh and had risen from death in a spiritual sense, it might have been an exaggeration by the writer.

There are a number of examples of Jesus not being recognised after He rose from death. That makes absolutely no sense. I believe that this is because Jesus did not rise physically from death, but rather in spirit and as His followers began to Teach as Jesus had taught them they realised that Jesus had indeed risen from death in that His words could not be silenced.

The truth of Jesus was His word, not His flesh, the only resurrection that truely counted was that His Teachings were not extinguished by killing His body.

If you look at Luke 24:13 - 35 / John 20:15 / John 21:4 you see a pattern of failed recognition of the risen Jesus. Now all sorts of reasons will be given why this is the case, the only answer that makes sense is that Christ rising from death was a spiritual event and those who after some effort recognised Him did so when they found that the Teachings of Jesus were still as powerful as ever.