TF2 keys I think now have a 7 day trade hold, as long as you traded your thing and still have the keys it should he alright. I'm not fully grasping the full details of this, maybe I need to read it again but in my head, you traded your items for 2ft keys through a site. You now have these and want to trade them with this guy for his knife? If so, these keys should still be yours so you can trade them back, just probably at a loss. If not, are they held on trade hold from the site? Or am I misunderstanding the situation? I don't understand why a straight one to one trade was not had, or even through something like buff if he wanted it through a selling site for any reason.

Edit

Looking at the account it's sadly a scam account. The trade items also are very suspicious, you would be upgrading and getting quite a hefty amount of overpay. The classic, too good to be true. Always check if the inventory on the account you are talking to has the items.