Honestly I can see the difference if only because I've now trained my eyes on proportions of people (unhealthy and weird I know lol) and the picture makes it to easy to spot these sorts of disparities. Two key things sort of pop out for me.
The first is the wingspan obliviously being the big key difference between the two that sort of make the guy on the right pop out more. It's noticeably shorter then his companion; of course this could be because he is only slightly taller.
This brings me to my second point: he looks noticeably frail in comparison. Now this I think is important because everyone has different body types (Ecto, Meso, Endo), so not everyone can look the same in comparison even if they have the same starting height and lengthen the same amount (I can elaborate more on this if you want). I honestly believe that if the guy on the right bulked up more he'd look better in comparison only because it doesn't draw as much attention to his limbs being shorter.
Last notes: his torso to leg length holds up pretty well. But If I was him I'd only have done 9-10 cm on both segments. Also if he did bulk up it won't be as easy to call out his proportions. Especially in public.
