1) Excessive irrelavent detail. The hoaxer thinks that an abunandance of detail lends credibility, but since the story is made up the hoaxer has no relavent detail, so in this case he gives details on his gun, and on his gun-scope, on how hot it was. The hoaxers are not terribly bright so when they fabricate detail that would be relavent (in this case somehow making a size altitude and speed estimate, and giving a time that fits with his descriptions) they usually slip up, as has already been demonstrated in this thread.

2) Irrelavent claims of authority without proof. (in this case he claims to be a physicist/pilot)

3) self aggrandizing details. The hoaxer wants above all else to feel special, typically they are losers and have to invent things to make them feel special. (In this story he claimed he was a competitive marksman, and also that he could have shot down this huge military craft with his 'Varmit rifle'- yeah right....)

In general anomalist, UFO, and conspiracy memes are seductive to those that desperately need to feel that they have some special knowledge- they cant satisfy that need in reality so they turn to fantasy. It becomes a drug they need to build their self esteem- that is why they NEVER question stories like the one posted above that fit into their fantasy. They NEED to believe it... It makes them feel important.