As others have stated, it makes sense that the V2L source would be isolated from the vehicle chassis, and it makes sense that the earth pin on the outlet(s) is connected to the vehicle chassis. That way, there can be no potential between any appliance metal and the vehicle metal; it would be easy to touch both at once.
EVs are an especially well isolated source, because they actually perform insulation monitoring at start-up (part of that set of muted clicks you hear when the car goes to ready or prepares for charging). So you can be fairly well assured that there is no leakage to the metal chassis from the battery. Unless you get an electrical leakage while driving, are forced off the road in turtle mode, and as you wait for a tow, you think "while I'm waiting I might as well use V2L and have a cup of tea!"
Even then, you'd have to have a fault with the jug, be touching the jug's metalwork, and also be touching some metal in the car to complete the circuit.
So it makes no sense to me to make a connection from the generated neutral to the earth pin of the outlet(s). But with the official cable including a Residual Current Device, it looks like they do make that connection. In my mind, the biggest use case for V2L is outside the vehicle, where the tyres effectively insulate the car chassis from earth, rendering the RCD pointless. But there are at least some use cases for using V2L inside the vehicle, and there you would often be insulated from the chassis by the seats and carpet, but there would still be plenty opportunity to make contact with the chassis of the vehicle. So for when you are inside the vehicle, I guess that the occupants are either floating, or at or near chassis potential. So inside the vehicle, or outside but touching the metalwork, the RCD does make some sense, and will protect you from faulty appliances that have conductivity from the live output to the metalwork. As noted earlier, if they didn't make that connection from neutral to chassis, there would have been effectively no danger, and no need for the RCD. Although I suppose it's possible that the vehicle's battery insulation monitoring might be conducted before every part of the vehicle's inverter is active, so there may be some potential risk due to a faulty inverter. It seems possible to me that a leak to chassis might not impair normal vehicle operation, and thus go undetected.
Outside the vehicle, everything is effectively isolated unless you have contact with the metalwork. But with that contact, it's the same situation as being inside the vehicle: you are protected by the RCD. I can't see how the neutral to chassis connection would alter safety when outside the vehicle. The RCD won't trip if you make contact with a live conductor, but you won't get a shock either. Any shock current, unless live to neutral, would register as an imbalance, so it would trip the RCD in case you did manage to get a connection through earth (perhaps it's pouring rain or heavy snow or there is an animal touching the metalwork).
But to me that raises a safety issue: if you opt for a cheaper option that doesn't have an RCD built in, then if as I assume the neutral output is connected to vehicle chassis, then it seems to me that you really should use an RCD to protect yourself while inside the vehicle, or one of the cases where something earths the vehicle chassis. Fortunately, it's easy enough to add one, but unless it's part of the cable, there is the chance that you'll skip using it when you actually need it.
Now it would be great to check that my assumption that the neutral and earth pins of the V2L cable are at the same potential when running. Obviously, this is non-trivial to do safely, so if you're not totally sure of what you are doing, don't attempt this. Testing for conductivity between neutral and earth when the V2L is not running is not relevant; there must be relays to connect neutral to the earth pin only when V2L is running. Otherwise, when charging, there would be a second connection from neutral to earth (the first being at the distribution/switch board), and this is not allowed, and can lead to nuisance tripping of RCDs as earth conductors share part of the neutral current.
