Or two ask in a different way:
I have sent Ethereum from my address to sell his address (see below), but I wanted to buy some token from him, not just sending money. How can I contact the seller (can I find him by his ETH address)?

From:0x591f6ebbc2dd9025d9e17b4e4237f1537c9aa033

To:Contract 0x8d12a197cb00d4747a1fe03395095ce2a5cc6819 (etherdelta_2)