I would think that any solvents would probably have long ago completely dissipated, I guess actual methamphetamine is a possibility(one news story mentions dry mouth as a symptom the family was experiencing) but it seems hard to believe enough would become airborne.
Other things like red phosphorus and iodine?
It makes vague claims, the only direct claim is iodine stains and human feces.
A friend, K, who works as a rental agent at a local real estate agency was telling me about their meth lab nightmare when one of their tenants was busted. By law the house had to be decontaminated before it could go back on the rental market and this meant removing every porous surface in the house - plaster walls, counter tops, floor coverings, everything. The place was basically gutted. They were permitted to retain and reinstall the stove after it was cleaned and decontaminated as it was non-porous (I think the wall heater was allowed to stay too). Much of the top soil in the backyard had to be taken away and replaced too because it tested positive for high amounts of chemical residue - the residents used to take their equipment out and rinse it under the tap in the backyard.
The tenant was said to be a seemingly respectable middle aged woman with good rental references. K said the whole lab fit into a wheeled bin and when they had their six monthly rental inspections, they’d just wheeled it into a cupboard. Until the place was raided, the agency didn’t suspect a thing.
I realise this doesn’t answer your question about what exactly was making them sick, but there was a world of difference between the article’s “fresh coat of paint” and K’s tale of demolishing the interior of the house. If the Aussie way isn’t an extreme overreaction, then it’s no wonder the new residents were getting sick. K stressed every porous surface and I’m sure she said they did extensive testing to determine the extent of the contamination, which backed up the need to rip it all out and start over.