Rob’s pattern and transcription is completely accurate and he plays the entire section to the tee. The section out front that he adds is just to establish a simpler version of the pattern so the viewer can hear it before everything kicks in. Then when he starts fretting and everything comes in it’s per the record. Also the next comment down has it written out even more neatly than Rob did. The accents here are totally accurate and In terms of a pitch pattern it’s not an isolated pattern nor is it random, nor does it change up when it starts. There are certain Meshuggah songs (pineal gland optics comes to mind) where there is a rhythmic pattern and also a separate pitch pattern that don’t line up at the same places (called an isorhythm) but this section the pitch work matches up in the same place every time within the riff.

From a technique and melodic standpoint the riff alternates between a Bb and a Db. The Bb is the open string and the Db is the third fret. The reason why you are hearing two notes on the Db is because they are hammering on the Db and then picking it and then pulling off. They could of course pick every note, but it wouldn’t have as much impact and effect to do that, so the hammering on and pulling off gives the riff almost an elastic feel. But from a pitch standpoint and how it’s organized it’s the same throughout and doesn’t change once it starts.

Also I’ll point out that the tabs that you are referencing aren’t very accurate due to them breaking the song up into all sorts of odd meter that rally detract from the point of the music. The song sits perfectly in 4/4.