"You can't bring anything through when you come—not weapons, not clothing, nothing."
If John Henry did jump, where is his clothing? It should've been in a pile on the floor, but it wasn't. Clothing doesn't go through, so it either gets disintegrated by the time bubble or left behind by the time bubble. Since Cameron's clothed body was sitting there in the chair (and the chair and table were there), we can rule out disintegration. She was clearly within the sphere of the time bubble when Weaver and John left, so she would have been within the sphere when John Henry left too. Yet Cameron's body was clothed and intact and John Henry's clothes were not there.
Was that a hint that he didn't actually jump ahead or was it just a gaff?