Graveyard

I walked into the room the other day, and Adam was drawing this picture of a graveyard. Whe I first looked at the picture, the gravestone had the date of "625" written on it. So, I asked Adam to tell me about the picture.
And this is what he said. "This is a graveyard, a graveyard in the future."
I nodded and said, "That's interesting."
We looked at his page together and he said, "Wait a minute." Then he picked up his pencil and brought it back to the gravestone on the page. He wrote a "0" after the 625, making the number "6250" and then he said, "Well, NOW it is a graveyard in the future."