Yup. The bass is a "Westone The Rail", and the pickup unit + volume control slide along it.
There is no tone control. You change the tone by sliding the pickup.
It looks well gimmicky, but it actually works extremely well, and of course the same idea was pursued by Gibson for a while.
The only problem is that, by their own admission, Westone's designers never really expected this to be a great bass or a top-end instrument so there was a certain amount of 'building down to a price' and this is particularly obvious with the crap electrics. I've replaced the cheap'n'nasty pickup on mine with a Dark Star ...