Compare is messed up on the seller's side which doesn't help at all here, but this sale is actually for 25 pure.

http://backpack.tf/profiles/76561198108148076#!/compare/1492819200/1492992000

Looking at the keys on the seller's side from the top down, the first 24 match the Mann buyer, the 25th comes from a bot, and the remaining 14 come from the Geezer buyer. The key that came from a bot was purchased by the Mann buyer shortly before with refined, some of which is visible here:

http://backpack.tf/profiles/76561197997985211#!/compare/1492905600/1492992000 - Buyer compare

http://backpack.tf/item/4999549496 - Refined

http://backpack.tf/item/3908667696 - Matching key

We can also confirm that the sale was 25 by looking at ID#s on the seller's side.

http://backpack.tf/item/2748957708 - 24th key, ID# 5724430120 when received by Squirrelnator

http://backpack.tf/item/3908667696 - Mystery 25th key, ID# 5724430124 when received by Squirrelnator, 4 apart from key 24

http://backpack.tf/item/4132989196 - 26th key, ID# 5724430195 when received by Squirrelnator, 71 apart from key 25

The larger gap between keys 25 and 26 shows where the cut off point actually should have been (compare has been grouping things incorrectly on rare occasion, I think when multiple trades are accepted in quick succession but I'm not sure).