Not same light gauge, as usual. I do think it has to do to a certain extent - TOO - with the angle behind a regular nut, at least at the first few frets. Here's an analogy. Far fetched but you'll get it.
Think of it as a rope tight over a gunwale (rail) aboard a sailing ship. It is tightened somewhere 14 degree angle downward away from the boat and gunwale. Think of PULLING the rope at a certain distance from the gunwale UP IN THE AIR. It doesn't require the same amount of force as PUSHING the rope DOWNWARDS the same distance, does it? Of course not. The angle at the other end of the gunwale, is helping to apply excess tension to the rope WHEN PUSHED in downward motion, ne's pas? Now when PULLING UP towards the air, the angle is not applying tension, since you actually shorten the distance and the line over the gunwale is straighter, thus, less force is needed.
Now, think of tying the rope with a knot AT or AROUND the gunwale of the boat. The rope stops there and does not continue behind it. Now, the same amount of force is needed to pull the rope UP IN THE AIR as it is needed to PUSH IT DOWNARDS since the angle remains the same in both directions. It may or may not be the same as in the former example.
Make similar comparisons to a locking nut on a bass, or headless, and a regular guitar bass with a regular nut.
Now, think of this AMPLITUDE of a string when struck. It surely can move more equally up and down closer to its end points than on a regular nut/bridge where the string carries on at an angle behind it. Hence the rubberband feel. But the actual tension of a string is the same since it is brought up to pitch.
It doesn't have to do with light gauge. The feel was immediately different when locking UP the locking nut on that guitar, and then the strings proceeded behind the nut in a normal angled way. Try this for yourself. Of course the actual TENSION is the same, but when plucked, and fretted at the closest frets 2-3 from the nut, the difference is felt. The amplitude alters a bit, that is felt especially when digging in and pick loud notes. Also, I would even go out on a limb and recommend even more relief on a neck with locked nut and bridge - and hence, headless basses too - than if they had regular headstock/nut/ and bridges. Due to the slight increase in amplitude of the string when plucked, hence "rubberband" feeling. Also this feeling is evident should one reverse a headstock, and let the thick e-string have a longer travel downwards towards the tuning peg which is further away - then - than on the high e-string. Must be same on any bass then. There's a certain subtle difference between TENSION and STIFFNESS that I think is misinterpreted around here.
This is probably called something in physics or mechanics law, I don't know, probably basic school physics, but can be put in under a few "categories" there.