Odd-looking but Human-like robots
In 2011, a civilization made first contact with a far more advanced alien species. As Samuel writes in his answer, the contact took the form of a robot meant to mimick the denizens of the less advanced species.
The robot in question was RoboBee, built by Tim Landgraf et al in a bid to learn more about the bee's language of dancing (2). Communication was one-way and only partly succesfull, yet a first-contact for the bees, in terms of communication. Their experiment lends credence to the argument in the question, that aliens would mimick us to make themselves understood. In the case of bees, a bee-like body was essential to get communication across at all. Also, the (to the bees) mysterious builders of the robot could not have survived among them in their true form.
I am RoboBee, ambassador from the human race to lesser developed species.
I have made contact with the natives. They are receptive but appear to be controlled by some form of hive mind.