On the origins of the lick itself (meaning: including the proto-licks mentioned)
One thing I found, and I’m possibly reading too much into things here, is that the set of intervals Falls in a major Pentatonic (3, 4, and 5). For some reason, it especially stands out if you put it in it’s second mode, which ends up giving you a Japanese Yo scale (can be seen on wikipedia here). Given that Far Eastern music (particularly China, Japan, Korea, and Mongolia) particularly LIKES Pentatonic scales, it’s not a stretch to say it possibly came from their fixation on them.
Now the Japanese scale I mentioned where it stands out, why that and not China, after all, that’s what it’s used most for? Well, I’ve definitely heard songs from other Far Eastern countries where it occurs, I played Variation on a Korean Folksong, it was DEFINITELY based around an ascending/descending F Yo Scale (went up and down 3 times, flipped between 1 and 2 and settled on 3). Of course, it’s entirely possible, even likely (as the Chinese use the major scale more), that it just came from the Major Pentatonic as well, I just wanted to point out it’s particularly noticeable in the yo scale.
My guess is someone heard one of the scales, or maybe even a song, and simply thought those intervals were a good way to go. You not only have a song slowing in rhythm, but you also revolve around the one spot in the scale with an abnormal tone change (Whole + Half step instead of just a Whole step), so it starts, goes onto what will be our final note slowing down to emphasize it along the way, seemingly “jumps” down, and then uses that little bit of tension to reverse itself, it sounds like a great musical idea. And I wouldn’t be surprised if that set of intervals hadn’t been emphasized in traditional music before for that reason. As for the harmony, It seems to be the easiest way to harmonize that particular scale, those are the notes that fit into the pentatonic most easily.
So in short: Because the intervals jump out so much, just due to their difference from the rest of the scale, and given that Pentatonic scales are rampant in that area, the riff itself is a really logical musical lick if you’re trying to represent something from that area. It has just the right bit of tension and resolution for musical purposes, and it emphasizes a scale widely used over there.
Or I’m stating the obvious/reading too much into it.