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Alas, in my opinion this person can be charged.
The Highway Traffic Act clearly has jurisdiction over any road the public uses even if over private land.
If however this person was clearly a trespasser and no one of the public used the road, then perhaps there is an argument. But if people use the road, whether private land or not, it falls under the legislation where careless driving lies.
Of course all law is fact specific and he should consult a lawyer. But, on what you have told me, the Highway Traffic Act applies and therefore the charge can be laid.