Very excellent and provacative question. Some thoughts...
If a natural body, it would unlikely be a "star", as we use the modern term. Of course God can do anything, but within the constraints of science (which of course He created), stars do not normally (ever?) roam, although their general trend is away from the center of the Big Bang. A comet, meteor or asteroid (the latter means "starlike", but is actually a small planet) would be much more likely, so perhaps it's just the writer lacking modern knowledge. But secondly, stars are usually much larger than planets, so a collision with earth would not be so much a collision as an enveloping. The smallest star discovered is still about the size of Jupiter, so while unlikely, a star smaller than the earth is possible.
Nuclear bomb: if it were, and was somehow "star"-like, it would be less likely an atomic warhead (which is fission), and more likely the same nuclear process that drives stars, namely fusion. In other words, an H-bomb. The amount of devastation described also supports a fusion device.
The passage clearly mentions conflagration before impact ("burning like a torch"). Objects falling from space burn up from friction as they encounter the atmosphere, so this doesn't really narrow things down. Realize if it were a nuclear bomb, it would likely be set off above ground (a so-called "airburst") rather than by ground impact, as this greatly increases its destructive sphere.
