This is the numbers station with the ENIGMA ID of E11, also known as the "Oblique" station.
There is no music associated with this station, and the station is not in AM. So the AM and music before the USB numbers started were probably a different AM station on frequency that ended about the time this started. If the carrier was still present when the USB numbers started you would have heard the numbers in apparent AM. 6280 is a frequently used pirate frequency and both Chinese CNR1 and the Sound of Hope also use the frequency..
This was a fairly normal null transmission. The format should have been something like this:
"THREE THREE ZERO Oblique ZERO ZERO"
This would repeat over and over for a bit over 3 minutes.
Then the station would end abruptly with "OUT" about 3 minutes after the start.
T!