Query account by CD-key

Hey, this morning I got a CD key for Cave Story+ on the forum.
Now I got 2 emails called "Steam account - Query account by CD-key"
Here's what they say:
This is an automated message generated by Steam account administration. It is being sent in response to a query made by a Steam user to discover all account names associated with this CD-key.
Steam account name: my acc name
You can use the above account name to log in to Steam. If you can't remember your password, click on the "Retrieve lost account" button on the Steam login screen.
The Steam Support Team

What does this mean? Is that guy trying to acces my account or trying to prove it's his account because it was his CD KEY?