Why is there a question mark after plane? My best guess is that the author is not a native English speaker. But he appears to be a New Zealander.
My thought on the question mark is, at a distance a flaming object seen at 1:30+AM their time would not be seen in detail.
His judgement on distance,50-70 km, was also non- definitive.
For an observer, Mchael J. McKay was on an Oil Rig, standing on a hill or tower 100 feet (30 m) in height, the horizon is at a distance of 12.2 miles (19.6 km)
http://en.wikipedia.org/wiki/Horizon
Any object at altitude, even above a few feet, past the horizon can be observed as long as it is bright enough and the sky is dark and clear.