Assuming this is the same person as in these posts, Sir Humphrey is right in thinking they are trying it on.
How about hitting them with a notice to comply, demanding that they repair their property so as not to negatively affect the appearance of the strata scheme?
But, to answer the original question, if the strata plans shows the driveway as part of the lot, then the lot owner has to prove that it isn’t – you don’t have to prove that it is.
Let them make the running on this and don’t spend a cent on legal representation. Just get a surveyor to confirm what it says on the plan.