It's not like the radar systems tracking these things on a day to day basis automatically classify something as a certain type or even size of aircraft. Even i

It's not like the radar systems tracking these things on a day to day basis automatically classify something as a certain type or even size of aircraft. Even if it were tracked by something, in that area of the world I bet there are quite a few "unscheduled" flights and it perhaps became something of routine. Or some remote radar operator is paid to look the other way on some flights, and mistook this for one of those. Most likely is that it simply wasn't tracked by anyone who cared, and especially not by anyone who recorded the data.