Your eyes see no difference.
Yeah, however your brain does pick up different signals, as there's more signals for your brain to pick up during 60 fps, compared to 30 fps. Whether someone's brain has aptitude to pick up 60 fps or 30 fps, possibly does rely on their visuocognitive ability. This might just be the cause of this whole debate, what someone can perceive could not be the same as what some other person reckons he perceives.
To say it more bluntly: maybe his brain is too slow to pick up these 60 fps signals? ^_^..