conventions in signals naming in datasheets
As you can read in the datasheet a write operation can be initiated (and terminated) with either CEx or WE#, whichever goes low last, thus you can have the two waveform alternatively; if the upper of the two waveform is CEx the lower il WE#, else you should read the upper as WE# and the lower as CEx.

In the datasheet, the notes from table 17 should be enlightening.