Sorry it's confusing, but for the "Pick 1 B" game, you get a prize if you match 0 digits only.  The prizes for each game are listed in the table on the right side of the page.

So if you pick 1 digit, and then click the A, B, and C versions, you see that:

for A: win if you match 1 digit
for B: win if you match 0 digits
for C: big prize for matching 1 digit, small refund for matching 0 digits