It's surely not out of context, Jesus believed that "the (apocalyptic) end is near" (Matthew 16:28) and he's the "Son of man" who brings it.

Matthew 16:28: (Jesus speaking:) "Truly I say to you, there are some of those who are standing here who will not taste death until they see the Son of Man coming in His kingdom."

At medieval times, people couldn't believe that Jesus could have told something that didn't happen, so they invented the legend that one of those present there still lives.

What you offer is the worldly perspective of Christ as a failed messiah. But Christ said that His Kingdom is not of this world. The disciples saw Christ come in His Kingdom when they witnessed the Resurrection. They saw the end -- that of the end of death and hades' dominion over humanity. They saw the ushering in of a new age: but not in the guise of a worldly conqueror, of a Rome-overthrowing messiah, but that of the conquering of death by humble love. Christ Himself demonstrates dying not only for those who love him but indeed for those who hate him.

Now you may of course feel free to disagree with this interpretation. But I think I have presented an understanding amenable to Orthodox Christian theology, which represents not an insignificant amount of people (200-300 million). I'm not trying to appeal to numbers, but rather my point is that when we are seeking to understand religious interpretations, we should be careful to not speak in absolutes such as "it's surely not out of context."