As an even more simpler explanation, portamento is simply a smooth slide between two notes (there's also polyphonic portamento, but it gets a bit more complex). What bandcoach was talking about was that when the interval between the notes increases, the slide has to be proportionately faster to make it to the next note "in time". In that Vybe example, I'm only hearing that single downwards slide (with delay), which could be accomplished by a number of things...not necessarily portamento, but it's one possibility.
The easiest way to figure this out is simply by taking a synth which has a porta/glide/slide (many names for this dear child) and trying it out. Make a simple melody line with some bigger jumps between notes (like, say, an octave) and then play around with the porta amount to see how it effects the sound.