Amplitude Response at greater than half the sampling frequency
This is a phenomenon called aliasing

https://en.wikipedia.org/wiki/Aliasing

Usually, there are anti-aliasing filters that will filter out signals with frequencies higher than fs/2.

However, in your case I think there isno anti-aliasing filter. Hence your 14 kHz-signal aliases to 2 kHz. Since f > fs/2, then apparent frequency = 16 kHz - 14 kHz = 2 kHz