How to stop grid resizing to window width without explicitly setting size?

ItemSize -> Full:

g2 = Grid[{{"Apples", "Oranges", "Peaches", "Pears"}, {100, 200, 300, 400}},
  ItemSize -> Full]

Import@Export["/tmp/foo.png", Magnify[g, 5]]    (* OP *)

Import@Export["/tmp/foo.png", Magnify[g2, 10]]  (* ItemSize -> Full *)

The option ItemSize -> All seems to work. The notebook looks like this

and the exported PNG like this