What they are saying is that outside of the"Fire Points" section of the rulebook, you have no permission to use anything while embarked on a vehicle.
The Fire Points section gives you permission to shoot while embarked.
Then you look up "Open Topped" to determine how that specific rule interacts with "Fire Points" in order to be able to even fire to begin with.
The Open Topped section says to measure from the hull, as there are no "specific fire points" on an open topped vehicle.
In order to fire though, you still draw permission from the "Fire Points" section of the book, and according to the new FAQ which specifically mentions "Fire Points" Anrakyr can no longer use his ability while embarked on the CCB.
I think this is an issue that will be hanging around for awhile. In the end, I think an open topped vehicle is considered to be one large firepoint. Whether or not how many firepoints an open topped vehicle has, it still acts like one. But this arguement is a moot point really. Simply read below.
However this pretty much sums up the answer about what is needed to do anything from a firepoint.
Is anrakyr using a power that ISNT shooting OR psychic and requires LOS? YEs
Is he embarked on a vehicle? Yes
If the answer to the two is Yes, then he cannot use the power - as it requires LOS and you cannot draw LOS from a vehicles firepoints