I apologize for my impatience. The original description really could plausibly be read to suggest he did not even check for bad input, and just assumed input was OK, maybe with assertions that would run in debug builds. It is true that not even coding sanity checks is less work than arranging to abort or throw, and marginally faster.

Producing faulty output is a more likely response to unchecked faulty input than crashing. It would have been better for the author to mention that, if true.