Yes, I would say that you're correct with that notion- we don't know in the question how many rugs that the original seller has to sell, so we cannot know if the goods are ascertained (if he only had 100 in stock) or are unascertained (Mr. W may have bought 100 of 500 rugs, but we don't know which of the 500 he specifically bought.)
So, if we presume that the goods are identified as originally being unascertained, it is now a good idea to read section of 16 of SoGA 1979, which will give you the basic idea to start from.
Of course, that seems slightly easy for an essay, doesn't it? There wouldn't be any need for the other people in the question if that were the answer. Rather, this first answer you've got is just one of many possible strands of the question. Imagine it as the first paragraph, where you say "one cannot know with certainty on the facts whether the goods are part of a larger bulk, which would render them unascertained, or are 100 rugs on their own. However, if they were part of a larger bulk, they are unascertained goods, and under section 17"...etc. Then explain the answer you just worked out with some cases added; try 'Re Wait (1927).
When you're done with that section, we'll try working on the next possible answer, based on some presumptions. Eventually, we'll cover all the possible answers; questions like this should be thought of as a spider diagram. How many words is this essay?