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Was there more than one key? Did he take any of the keys with him? It sounds like the engine immobilizer is activated and doesn't recognize the key you are using.
So I assume none of those keys work, a couple of things you can try:
Use the key to lock and unlock the left front door five times ending with unlock.
Disconnect the battery negative cable for a few minutes with the key in and in the on position
If I can think of anything else I'll get back to you.
Also try this:
With battery disconnect put the key in the ignition and turn to on
Leave the door open wait 5 minutes and re connect the battery
The grey key is just a valet key, that means it should work to start it but you can't unlock the glove compartment.