Im gonna give a slightly more detailed response than tsundere here.
So number one on the site is missing 13 pets:
4 unreleased, 3 from upcoming world events, 1 from fishing shack.
5 only released in China
3 only released in Korea
1 only released in Taiwan
Of the five people on 4143 points (who share 2nd place) two are from US servers, while number one is from EU. what they are missing are the two EU exclusive pets, Gurky and Lurky. So those two have all pets that has ever been available on US servers.
The other three are from the EU, and are also missing Gurky, as well as Murky (the first blizzcon pet, and incredibly expensive).
Sorry for the long and boring answer, which is same as Tsundere above said, but can at least I hope it was informative.