What generation of the Apple Pencil does this case work with?
Apple Pencil Case 1.0
Speculating… when there are currently multiple gens of a device and the standard text does not refer to a specific generation, the item in question is first gen. That is, when the item was current, there was only one generation.
I believe prior sales of this Apple Pencil holder confirmed it is for first gen Apple Pencils.
Yes, the case is specifically made to house the first generation of Apple Pencil.
And your speculative banter about there having only been one iteration of the product at that time is both accurate, and amusing.
Back to the pencil case though - I have a few of these in use between my wife and me, both having the second generation Apple Pencil. The fit is “wrong” in that the case is longer than the newer, magnetic pencil, but it’s otherwise snug enough that I didn’t mind buying a couple at the heavily discounted price, just for the sake of convenient protection; Whenever we take the iPads out to work, or on a trip, it’s nice to have a case so that the pencil tip doesn’t get damaged while in a purse or bag. We still just keep the pencils out, and use the magnetic charging and attachment around the house though. This sort of case is not necessary, by any stretch, especially for the newer, second generation pencil. But it does give me peace of mind.
Hope that helps 
For previous comments, see this older thread for the same product:
[Apple Pencil Case (Your Choice of Color)](Woot forums - Apple Pencil Case)