Yes, given the old "other things being equal" but the point is, other things are never equal in these adjustments. His elbows may be bent more or less, his back may be straighter, his shoulders less hunched, wrist orientation, etc. My experience is that the technical explanations about "why" from bike fitters are not often satisfying, but there are reasons why specific changes usually lead to certain results.

If you were to diagram the force vectors, using a decent approximation of weight distribution in the upper body, I think that we would find that the change in stress in the shoulders, or arms, or hands, is just about insignificant either way even given various assumptions about position changes. Because of that, I surmise that the changes in position (which we'd be making assumptions about) are more relevant than the change in weight distribution.