As usual, math and logic has defeated romance! Unless the article states when the picture was taken.
Most horses do not live past 30. Ponies yes, but only a few horses. And for back then with no parasitic care to speak of and other things, life could be short indeed. That horse is looking mighty frail and is underweight by several hundred pounds. Very old horses (and a lot of mammals) just lose the ability to digest nutrients and get thin no matter what and go downhill from there.