It is my understanding that three faulty Centaur burns occurred within a 90 minute period, which I believe would have ended about 50 minutes before the Namibian sighting at 19 h UTC, so a venting seems more likely than a burn. Clearly, this orbit is very rough - and not just because I don't know the exact location of the observer. But there is likely a range of arguments of perigee that would fit. Moreover, since the Centaur was out of control, there is no reason to believe that its burns were coplanar, so the inclination likely is much different than the one suggested by the launch azimuth. The story is interesting and has some possibilities, but as long as the cloud did not move, then I do not recommend that anyone waste time trying to search on the above elements.
Lets see what additional information emerges.