I’m not sure what you mean by ‘smooth’ exactly, but perhaps you are approaching things differently. If you automate the filter frequency then you can achieve different results (which are sometimes awesome), but you can also run into weird behaviour when the frequency is sweeping all over the place. In this particular tune, it sounded like the filter frequency remained pretty stable while the volume was automated instead.
It’s also important to note that in many ‘wobble’ sounds, the wobble does not come from the bass itself, but rather from a mid-range sound layered on top. This way you don’t ruin the characteristics of your bass sound, allowing you to get really crazy with the harmonics of some higher frequency sounds instead.