No. It's not a problem of salt, but the salt partecipate to what is happening.
What you see there is typical electrical corrosion happening underwater: electrolysis. I work with ships, and know well enough the problem.
When this light is switched on, the ground (or -B as you prefer to call it) is from the cell bottom to the tailcap, and tailcap fully tightened makes contact with body, so also body is grounded, the ground then goes to driver and led. The + pole from cell goes to driver and led. The circuit is closed and the light is on. There's no difference of electrical potential between body and tailcap and no corrosion happens.
But when the light is off, the ground is only the tailcap. Not being fully tightened means no contact with body, so body is not grounded. So what happens next? Happens that + pole goes through driver and led, and to body. The circuit is open between tailcap and body. That is easy to figure out, anything that can electrically connect body and tail, will let current flow, and light will switch on. Well, when the light is on air, the air is relatively dry and a very bad conductor, so no problem. But when immersed in seawater, the salt rich seawater act as an electrolyte, and happily flows electrons. The body and tailcap are acting as anode and cathode, the cells supply the power, the seawater is the perfect electrolyte to the job: the anode release electrons and the electron-deprived metal corrode and dissolutes in the water (pitting), the cathode receives the electrons and in the area builds up a layer of whitish minerals from the water.
As soon as the cell can supply current, the corrosion will not stop, untill the cells are depleted or all the metal dissolved. The higher the current rate the cells can supply, the faster the corrosion. The anodization prevents the aluminium from corroding in air atmosphere (anodization is an induced passivation, which is electrically inert in air), but can nothing when in seawater, because the chlorides (salt) dissolve the alu oxides forming the anodization.
The next bad part of the figure is that there's no real solution to this. The use of a mechanical or magnetic switch (rubber booted) and keeping body and tailcap grounded (electrically connected) will anyway slow the corrosion rate by an enormous margin, eliminating the current dispersion.
Note anyway that alu in seawater will corrode, and any scratch to the anod is a good starting point.
Note also that most frequently used alu "light alloys" are not suited for seawater immersion, because of copper content. The alu alloys for marine service are special alloys low on copper and high on magnesium and manganese. Can you bet, they are more expensive than other "normal" alloys for terrestrial application, so I can hardly believe a flashlight producer will invest in these. Much easier to use PVC or other high tech "plastic".