Not quite. "Author's assertion" does refer to some kind of claim the author is making (in this case, that something called "job evaluation" is a useful technique for comparing dissimilar jobs). When we qualify something, though, it means that we're either (a) acknowledging some kind of weakness in our argument or claim, or (b) limiting the scope of our claim (eg, "this only applies to high-tech companies"). (These two things can kind of be seen as the same thing - if you have to limit the scope of your claim, that is a weakness.)

So, in this case, we're being asked to find some kind of limitation or weakness in the author's claim - something that the author actually admits ("admission") in the passage, not something that we just think of on our own.