Well, not necessarily. And certainly not as of 2005.
Nathan East with his California 5-string, courtesy of Kala
The small-scale hybrid bass concept is not entirely new. The Ashbory came out in 1986. It uses polyethylene strings to cut the length down to about half that of a standard bass. And then there's Paul McCartney with his Höfner 500/1 (a bass neck on a violin-like body.)
One of the many experimenters over the years is Owen Holt, and he combined a baritone ukulele body with pahoehoe strings (manufactured under his own Road Toad branding -- which name is a reference to the infamous Cane Toads, by the by). He then took the new instrument to Mike Upton at Kala, who had learned ukulele building in Hawaii before returning to manufacture them in California.
The first u-bases were acoustic-electric, constructed not unlike a baritone ukulele. There was some experimentation with truss rods along the way, as bass applies new stresses to the standard uke construction. Somewhere around 2011 Kala brought out a solid-body four-string, and in 2015 had five-string options (as well as fretless and left handed options).
Bass players are converts (or, at least adding it to their collections). I saw a used one at the local music shop and was struck by how odd, cute, and friendly it was (in that, at least, it clearly shows its ukulele heritage).
So, yeah, I bought it. And it is, fortunately, one of those instruments that is easy to pick up (all instruments are a lifelong project to learn to play well.) Ukulele skills translate, as do, oddly, violin skills; the former is in the fretting and plucking, the latter is in the sensitivity. This is not a an instrument requiring you to haul down a thick steel string by sheer finger strength. It is an instrument that registers every fretting finger, every brush, every tap.
The one I got is the Kala sunburst SUB. It looks like a baby electric guitar. It has that Fender solid-body shape -- but an oversized headstock and four thick black gummi-worm strings that look like something that belongs on a toy. Internal pre-amp with volume and two tone control knobs on the front and it is just slightly larger than my e-violin.
It is tuned like a four-string bass and with the 20" short-scale has almost the same range. You can hold it like a ukulele but finger plucking is easier with a guitar strap. With those Road Frog Pahoehoes it has a jazzy upright bass quality (particularly if you thumb-pluck and use the heel of your hand to further reduce the sustain). I'm told that with the optional wire-wound strings you can get more of the aggressive bite of a bass guitar.
It is also almost completely silent when not put through an amplifier. You can't even practice it unplugged (but VOX makes a cute headphone amp for guitars and basses).
I do have what appears to be a set-up problem, possibly inherited from the previous owner; my middle strings rattle. I've emailed Kala and will probably be replacing the nut. The low tension means bending is difficult and snapping doesn't work (slap bass technique). It has frets so slides have that fretted sound and you can't really do vibrato. However, the sensitivity of the pickups makes hammer-ons and pops extremely simple. In short there are still plenty of techniques open to exploration on this instrument.
So I've rethought how I will be approaching bass in my next recording project. I've been aware for a while of the true expressive quality of the bass, a quality and a realism that synth patches are a poor substitute for. Well, my playing isn't much better. But the u-bass makes it just possible I can do those parts live now.
And a u-base doesn't take up a lot of space.