Steam URL: Steam Community :: 76561199035839881
Backpack URL: https://backpack.tf/u/76561199035839881
I copied his backpack URL into my browser and it was the same private inventory, so I would assume that this person is a legitimate TF2 trader who has been hacked, or he is a very successful scammer.
when these guys exercise these scams, they use very crude mental warfare - they will get upset, or irritated or impatient with you. This is to prey on your anxiety and scare you into making bad choices without rationalising it. Never trade away items to a site/bots like this, this is for sure a scam and this person was trying to steal my items.