I do agree that it’s law.
My point would have been that when the constitution was written, countries weren’t conferring citizenship on offspring of people who’d left their country. That seems to me to be the thing that changes, and it also strikes me as arrogant when another country says “you are our citizen” when you have no wish to be.
What is also worrying is that ministers knew about Parry’s concerns and did nothing. And the Coalition are dumb for not having an exhaustive checklist, and/or discussion with a lawyer versed in such matters before being preselected.