Granted, but this proves nothing.
Oh come on. The cross-hatch does not look even remotely like the saltasaurus's armour. The saltasaurus's armour had protrusions from it, which are not depicted by the cross-hatch. In any case, you haven't explained why the drawing's back has a much more pronounced dome shape, nor have you explained why the shell/armour has a straight base rather than a contoured one.
What do you mean the Brachiosaurus had the more generic head shape? The drawing on the stone looks like the most generic one of the lot. It is simpler in form.
My whole point is that the drawing is far too stylised to be able to identify it as a specific species of dinosaur. Your claim that it can only depict a saltasaurus is simply not realistic.