The point is that you said:
And that guy said after watching footage shot natively at a high fps:
Not saying it's the same but it is similar.
It is similar in that sense that you get a new frame 48 times per second. The detail, blur and motion will differ. Also, this is one person's opinion after watching ONE scene shot at a high fps. If he had compared the same scene shot in different frame rates, than he would be onto something. He also says that certain scenes look really amazing (like slow motion).
Some people claimed upscaled DVDs have similar quality as Blu-rays. That is totally bogus and you can see that with your own eyes. Unfortunately there is basically no movie footage available in 48/60 fps which makes it impossible for us to compare. Hopefully we can do that when "The Hobbit" is released.