You nailed it with your assessment - full, harmonic, wide - boom!
I don't think he's using chords, mate, but he's definitely got some nice harmonics going on to widen the sound. He might have a few oscillators going on - maybe not quite sure of the tuning, though - I only listened to the first one and I don't think the tuning is as much as that (although I could definitely hear a sub in there, which could be a sub-oscillator which is likely pitched -12 semitones down).
The oscillators could be pitched a few cents apart, or he could have some un-synced oscillators widening the sound (or both). He could be running some widening FX on there, like a subtle chorus - man, could be doing many things.
It IS a nice sound, mate!
Personally I've never used chords for bass - to me it makes the low-end sound muddy and messy - awash with too much low-end energy.
