18000 pesos per month for groceries seems reasonable, I don't have exactly comparable figures, but vegetable, fruit and eggs for 2 people in La Monumental works out at around 5-6000 per week depending on what you buy exactly. Out of season and imported fruit is more expensive. You can pay more for organic fruit and vegetables (El Tallo Verde or La Palta Sagrada), I think that would come to around 9000 per week, again for 2 people. A week's supply of chicken and pork from Ovo comes to around 3-4000 pesos for two. Beef costs more, but we'd buy that only for a BBQ maybe 1-2 times per month. My wine budget is probably more than for most people so I won't go into that
Otherwise our food needs are sporadic, buy coffee, spices, vinegar, olive oil every 6-8 weeks. We do a lot of cooking at home.
In summary, I guess excluding wine we pay 5000 per person per week to eat really well at home, not too far from the figure mentioned. I thought the article was fairly accurate, obviously from someone who's here in BA, not like the one by the clueless git who figures beef is served on skewers and the Kirchners are Jewish.