Hi Rafael,
The noise specifications in the datasheet are input-referred. Make sure to select the checkbox "Analysis data is input referred" near the top-right of the screen. The last image shows results for a gain of 12, correct? Some channels are still slightly high after dividing by 12, ranging from 2.31 uV - 2.98 uV, but they are much more reasonable. :)
Also, just FYI, when you configured the channels as Input Short on the front panel, the internal MUX is configured to short the inputs internally. This is why you did not notice a difference after shorting the external input jumpers on the EVM. When you start using an external signal source with cables, a neat test might be to short the ends of your cables, configure the ADC channels as Normal Electrode, and measure how much noise is added to your system in comparison to the internal short measurement.
Best Regards,