Edit: To be clear, it's not necessarily a melody using only the smallest stepwise motions through a scale.
By my reading this contradicts what you describe in the title. Your "edit" note and continuing description make things unclear, because nearly all music will involve lines that go up and down in short conjunct segments along with some leaps.
It's hard to know what you mean, because your not really describing in musical terms what in the music you're focused on. The extra words like 'tumbling, surging, juicy' don't help either, not until those words are connected to the musical devices that produce those feelings.
The step-wise motion you describe in the title would be called conjunct motion. Disjunct motion is moving by leaps. Both of those terms are generic and don't get into things like rhythm, length of the passage, or tempo.
Conjunct motion of short duration, like 1 beat, might be called various turns, and German has many specific turn names based on the contour of the turn. There is another German term, fortspinnung, for stringing together short turns and other motifs. It's associated with German Baroque music.
Those are the terms that came to mind immediately upon reading the title of your question.
When I listen to the recording example all of that goes out the window and I immediately thought: minimalism. When the track continues to the electronic dance music beat it isn't really minimalism, but the first 10 seconds sound very similar to stuff like Steve Reich's Piano Phase.
Phase and phase shifting seem like terms to apply. The idea is to take a fairly simply motif, repeat over and over and over in more than one part, phase (or time) shift the two parts slightly to create a composite line which has new melodic features. Things like dissonant seconds create rhythmic accents, or you can start to hear repeated pitches, things that aren't in the original motif played alone. Minimalist music achieve the phase shift in actual performance, the players would sort of go out of sync rhythmically. Your sample track does something similar, but it's using some kind of electronic delay.
In your example, it's hard for me to aurally separate what actually was played (probably on a keyboard) from what was generated by delay. I don't know if that matters to you, but personally I want to separate what was played from what any effect settings were, because I would want to know how to do it. That might have some bearing on terms to describe it.
One thing I hear is a polyrhythm effect. Polyrhythm is playing two "conflicting" rhythms simultaneously like groups of 3 against a base of 4. The performance versus effect question comes up hear, because I can't tell if that is played or just the result of the delay. Regardless, polyrhythm may be a term to apply. It diffuses the sense of meter, and with out the solid feel of a well established meter, this might account for what you hear as "tumbling/surging." Also, when meter/rhythm are diffused it lends for a lot of repetition, because it's harder to aurally identify the repeating pattern.
You probably want to not describe with as chromaticism, because this stuff sounds very diatonic. In fact if you do this phase shift, delay on actual chromatic motifs, it will likely create unpleasant dissonance. Harmonically this stuff isn't that exotic. In modern styles harmony pretty much extends to playing nearly all diatonic tones together. A diatonic thirteenth chord without the eleventh is pretty normal provided certain voice spacing and inversion aspects are handle right. A strong, clear bass part - which this example track has - with nearly any combination of diatonic tones in the upper range/voices can work well. I don't mean the upper parts are haphazard, we can't discuss everything in a Q&A, but you can generally say the upper parts can enjoy much more freedom that the bass. You might say there is a kind of board interchangeable tolerance of tones in the upper parts. I think that free treatment and tolerance of dissonance, when confined to a diatonic palette, in the upper parts contributes to the "twisting" and "colorful" sense of the music.