By the looks of that picture im going to agree with mark that you might have had a steep angle dry shaving your arm hair. Shave testing on a lathered face is the only true benchmark on how a razor performs but I find that a well honed edge will cut hair on your arm even above skin level. So maybe next time try to just graze the hairs on you arm just to see if they pop as you hover the blade a little above the skin. I personally always felt that stropping wont hurt your edge and should be relatively forgiving to the blade as long as these criteria are met 1. No bearing down on the blade it doesn't have to be feather light but just be mindful of weighing down the blade with your arm and deforming the strop, not good. 2 Holding the strop taught. yes it also doesn't have to be where your knuckles are turning white and your ripping the screws out of the bathroom wall, just tight enough to make the surface flat and your stropping should keep it relatively flat. 3. Spine stays on the strop. when turning the razor or stropping, the spine stays in contact with the leather, If the spine comes off the force is transferred directly to the edge and your done its blunt. That said stropping can look rather brutal otherwise. I remember many years ago watching old Italian barbers in my neighborhood stropping before they shaved the guy next to me and it looked rather violent. A lot of cracking and popping of the razor on the leather at high speed and then he shaved his client without a complaint. All very artfully done with a bit of showmanship to boot.
