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Planes have a radio device called a transponder. Each flight under airtrafic control is given a four digit number to dial into the device. Each time air traffic control radar is picked up by the device it trasnmits the four digit number plus the planes altitutde. The transmission of this four digit number is called squawking. As in a controler instructing a plane, "Piper 1234 Zebra squawk 3241 and ident". The pilot would dial in 3241 on the transponder and press a button labled ident. This identifies the plane with a blip on the radar screen.

If the pilot accidentally dialed the wrong number or failed to call controlers when he entered US air space the jets would be scrambled and he would be diverted.

It is possible that he had a radio or electrical problem and could not call to get a number. In the old days if your mike or radios failed a pilot could fly to his destination and land using light signals.

I have not been able to pass a flight physical for 8 years, so I am not up on current regs.

But he was apparently squawking a wrong number or the controllers couldn't talk to him.