The same history has other sales

https://backpack.tf/profiles/76561198191744974#!/compare/1780704000/1780876800

https://backpack.tf/profiles/76561199564942025#!/compare/1780617600/1780704000

Dumped to STN, nothing matches

https://backpack.tf/profiles/76561199564942025#!/compare/1784851200/1784937600

https://backpack.tf/profiles/76561198106495563#!/compare/1784419200/1784937600

33 keys match via near IDs in seller's compare, in the buyer's compare, 11 keys and 1.66 ref match.

STN currently has a buyout of 12 keys however they change their prices all the time so it isn't reliable enough to use. To be sure the sale was actually 11 keys, you can ask the person you bought it from how much they paid along with a screenshot, but a range will be needed in any case