No, by short walks, I meant hand walks not ridden walks, he's not in good enough condition to be ridden.
Also, just letting you know in case you hadn't noticed, that saddle doesn't fit at all. It's sitting way down on his withers and likely pinching his shoulders due to the bars being too flat and the gullet being too wide because he's seriously undermuscled and underweight.
Frankly, I think he's an absolute angel for not bucking you off because that was no doubt extremely uncomfortable for him...if not downright painful.
Please, don't ride him again until he's in much better shape...and make sure you know how to make sure a saddle fits before you use it.