Continuity mistake: In the end of the movie, Hilts (Steve McQueen) is returned to the camp - he is dirty and his shirt is torn. When he enters the cooler, after being tossed his baseball glove, he is clean and his shirt is no longer torn. (02:49:50)
Continuity mistake: The position of the propeller crank changes between when Hendley first hands it to Colin and when Colin begins to crank it.
Continuity mistake: In the scene where Roger, Mac, Danny, and Willie are trying to figure out how to dispose of the dirt from the escape tunnels, Willie's motionless hand on the tabletop jumps from the supine position to the prone position between shots. (00:51:10)
Continuity mistake: In the scene involving Hilts and his baseball directly after Sedgwick and Haynes have their sham fight, Hilts drops his canvas bag with his name on it on the ground. When Goff comes to join Hilts, however, the canvas bag is nowhere to be seen. Despite the angle it would have been seen as the bag was placed down horizontally. (00:13:35)
Continuity mistake: When Hilts tests his blind spot theory at the wire and is caught by the German guards, in one shot he points at the wire with his thumb. In the very next shot, his arm is instantly resting on his hip. (00:20:00)
Answer: He could have only known a small amount of German, enough to answer a question or two, but not enough to carry on a full conversation. Also, the German seemed to be wanting to have a full conversation with him. He was on the run and didn't have time to talk. He was most likely being a smart ass saying he knew German.