I took this a couple of days ago so I may not remember it correctly, but I think that since the apparatus was different from an actual kidney, there were slight (though this could be major) functional differences. One major difference was that the pores in the dialysis tubing were only a certain diameter, such that only certain-sized molecules could pass through it. The diameter given was rather small; So small that proteins could not pass through the tubing. I was pretty confused after reading the passage as to how the proteins were filtered out by this mechanism, if it was actually supposed to be efficient. But, IIRC, nothing asked you about whether or not the apparatus worked properly or not. Since you were given no evidence of how proteins were filtered out, I think you had to go with the assumption that you didn't lose an appreciable amount of protein during the process, and therefore the protein content would remain very much similar to the original protein content, and the relative concentration of protein may be the same, or even higher than initially, since other solutes were indeed removed.
Hope that made sense. This was a weird passage!
