Keys were unrelated to that trade, check their history. Also, look at the backpack from the side of the other person involved in the trade. You looked at it from Ciosek's inventory. So let's take a look at it from Arcslayer's inventory as well.

http://backpack.tf/profiles/76561198044934255#!/compare/1491609600/1491696000

Looks like the Strange Professional Killstreak Skullcutter, K-a-W Tom-o-Shanter, and the C9 Spartan were all involved in the trade (We can see this by going into the histories of those items and seeing that they are being given to Arcslayer by Ciosek on the same day as the trade for the PC Ground control.). That's 44 keys in total.

So is this kind of thing on us for not double-checking trades or is it a problem with backpack.tf? I really hope this doesn't go through because that's an absolutely monstrous unjustified change.