I am not sure I understand what you are meaning. Because it is the same signal being displayed in both cases: to get the second window, we selected the signal from the first recording and did ‘displayed selected channel’
So the amplitudes should be exactly the same in both case. Note that, when we load the file in Matlab, it is the second amplitude that is being displayed ( -61.21 muV in this case)
[Edit] It seems the difference arises if we use the average reference montage in the first plot and is not present if we use [all channels]. But i am not sure it should matter in this case, as we already applied the reference montage to the file (using standardize > apply montage)
In this thread ( Apply montage or re-reference EEG ), @Raymundo.Cassani seemed to indicate that applying the average reference montage twice would have no effect on the signal ?