pH does not equal total acid content; and the two value are not always well correlated either.
pH measures how many H+ ions are currently available; total acidity measures how much is potentially available. As available ions are bound, more become available until the total acidity is finally depleted to 0.
I don't know how the canning recipes are formulated. But it would be important to understand which measure applies.
That said, considering that tomatoes are considered sufficiently acidic for water bathing, it doesn't seem to take a whole lot of acid to make things safe.