How the pitch shift works here
Shifting pitch without touching tempo takes two FFmpeg filters working together. First asetrate changes the sample rate the audio is read at, which moves the pitch up or down but also changes the playback speed as a side effect, the same way a turntable sounds higher and faster at 45 RPM than at 33. Then atempo takes that faster or slower result and time-stretches it back to the original duration, cancelling out the speed change while leaving the pitch shift in place.
With Keep the Tempo switched off, the tool stops after the first step: asetrate alone, so you get the full turntable effect, pitch and length moving together. That mode is a genuinely different sound, not just a shortcut, because there is no time-stretching involved, so it stays cleaner at large shifts than the tempo-locked mode does.