I'm alone. I receive a trade request. How?

I've been in my hideout for hours now, mapping, then suddenly I get a trade request from some random player with Chinese characters in the name. I decline. I walk around my tiny hideout for a while, there's no one here, and there's no text about a player having left the instance.

How did I get a trade when no one was nearby to trade? I've never seen this before in PoE1.