No worries.
I've just phoned home to speak to the head of domestic operations and discovered the letter was prompted by guidance here:
Health Emergency - Information for schools
and also by the fact that W.A. had its first confirmed case today.
With regard to travelling parents, the link above advises you to contact your school for advice. Our local education authority (W.A.) has decided that in the case of travelling parents then the 7 day exclusion also applies. Maybe other states will see this differently.
Effectively it implies the kids should stop going to school or I stop going to work until this is over. They obviously haven't considered the case of airline crew and similar regular overseas travellers. I've asked the principal when we can expect the home tutor to start visiting!