They might have been able to afford food, but not the kind of food they are accustomed to eating. Someone paying $400 a month for Crossfit probably isn't checking out the bargain aisle at the greengrocer and supermarket. It'll be organic free range imported fair trade gluten-free palaeo something.
The average Australian household with a couple and youngest child under 5, like us, spends AUD282pw on food [
source 1]. We spend 130, and we drink small amounts of alcohol, eat meat, fish and dairy, etc - we just don't eat out, really.
We don't really think about it, but essentially we're on a GST-free diet. Sales tax in Australia does not apply to fresh foods [
source 2]. At shops when you get your receipt, stuff that had GST has an asterisk; if those are all missing then you probably have a diet which is both cheap and healthy, however you'd have to cook it. For example, dry or fresh pasta noodles, onions, garlic, cream, mushrooms, raw chicken, chicken stock and pepper do not attract GST, but "Hand-rolled penne with Gippsland mushrooms and chicken in a creamy sauce" for $22 at a restaurant does.
I would expect that people who have lifestyles of a lot of travel, Crossfit and so on, will also be contributing lots of GST to the tax office, and spending much more overall. After all, if the average is $282 and we're spending $130, then to keep the average up, someone is spending $424.