Why did David not trust the man who wanted to help him escape?

The man was a guard and was supposed to keep prisoners in the camp, not help them escape.

Since he was a military official who David doesn't know personally, but the commandant knew David because he has seen him grow up. He knows that David is an orphan with absolutely no knowledge of the outside world. One day he is moved by compassion to turn off the electric fence, to give David some supplies, and to help him escape.