I don't see how it would be possible to fire it by any kind of manipulation of the frame or slide. The slide covers up everything. There are a lot of ways a defective gun could fire tho.
I am not an expert on the PPK. Mine was made in postwar France so it could conceivably be slightly different from German wartime guns.
Impossible to say from the article, but today's PPK's are made under license by S&W. If I remember correctly, they were banned from import because they were 'too small' and were considered a 'Saturday Night Special'.
Although, how a $400 to $500 handgun qualifies for that is beyond me...