A man just negative me for scam. is this a scam?

I have a thread in trade section http://www.steamgifts.com/trade/jhMiC/h-bundle-games-w-4-5-cards-gems-refs-and-offers
and today this man come to my thread and leave a message:
http://i.imgur.com/L8dKSV5.png
As I don't have the game, I answered:
http://i.imgur.com/9gPWcog.png
The man reply that he want frozen synapse instead:
http://i.imgur.com/OZtohz4.png
I answered:
http://i.imgur.com/wUCAWnu.png
And of course, spy chameleon is 4.99 euros and my frozen synapse is 22.99 euros, They are all bundled games and not worth the money but it's clearly the base price is far from equal.
This "game" means other game of equal price. I mean he can trade my frozen synapse with a certain amount of cards or a key of game, but I never said that's his spy chameleon. I never tell him to give me his key of spy chameleon for my frozen synapse.
The man then add me on steam, here is our chat, he said that I try to scam him?!
http://i.imgur.com/lkfQj7j.png
Of course I won't trade frozen synapse with him, it's totally not equal, and he say that I try to scam him, and leave me a negative:
http://i.imgur.com/Co4yvvj.png
How I scam? I just tell him that he can trade frozen synapse with cards or game, but the "game" is an equal game, I never said spy chameleon for frozen synapse, I never see any of his code, and I even don't have scamed for anything, and he negative me for scam? I think this is really a stupid thing.
So what should I do? Send a ticket to admin? I think this is very unfair for me, scam? I even don't get anything from him!
(no name in pic now so this is allowed?)

Edit: Just send a ticket.