How much is this film based on true event?

I hate to say this, but is this crap really based on someone's autobiography? I mean, if this is from someone's real experiences, how could the writer, director messed it up with so many cheesy plots, like all the action scenes, all the chasing scenes, all execution scenes and, yeah, the pilot had to kill a German solider, sleep with a local girl and bring sexual awakening to the coming-of-age boy. Wow, is this the realism that some critic had praised for?

And how could the boy be so retarded to hand over the pilot to someone so fishy from the very beginning? If this is realism, how could the filmmaker keep suspension in such unconvincingly stupid way?