How did the author survive Auschwitz?

The narrator, Tadek, is a Pole sent to the Auschwitz death camp despite not having been involved in any resistance activities against the German occupiers. But then, the Nazis are not renowned for being overscrupulous when it comes to establishing guilt or innocence. As far as they're concerned, Tadek is a Pole, a Slav, and therefore a member of an inferior race. The Germans feel entitled to treat him however they please.
Although Tadek isn't a Jew, conditions at Auschwitz are still unspeakably bad, and he's treated accordingly. Nonetheless, he somehow manages to survive. The main reason for this, as Tadek tells his fiancee in a letter, is that the Germans stopped gassing non-Jewish prisoners over three weeks before he arrived at the camp. With the Soviets fast approaching, Tadek is taken by the SS along with a number of other prisoners to Dachau concentration camp in Germany, where he is eventually liberated.