Cattle Decapitation - Guitar & Bass riff matching / Tuning question

Hi everyone !

While looking for Cattle Decap. tabs i found out that guitar and bass play the exact same riff (same fret position on the lower string) but the guitar is a six-strings tuned D# standard and the bass guitar is a five-strings tuned G# D# G# C# F#.

Here is the tab in question

First riff : guitar start playing fret "4-3" (G#-G notes) while bass (lower string is G#) playing exact same fret play C-B notes.

How can it sound good while not playing the same notes ? It certainly related to music theory but i need help for this one.

Cheers r/Bass !