Well, I did think the substitution argument was interesting, that groceries are increasing at a more rapid rate than restaurants. I would imagine in addition to the reasons given that it's a combination of restaurants having higher profit margins and/or being willing to cut into them because their customers are more sensitive to price changes (whereas, if prices go up at the grocery store, what are you gonna do, not eat?). When food prices went up a lot around 2007 I noticed myself being more willing to pay for, say, expensive truffle chocolates, because they were only two dollars more than bar chocolate. Or more willing to buy avocados because bananas were more expensive--in other words if I'm going to buy the lesser product that I want less, I better be saving a lot of money to compensate for it. Once I'm saving less money, the motivation diminishes.
And to be fair, unlike a lot of this type of journalism (and what do we call it? Not sensationalism, it's not a large enough scale for that. Catty journalism? Debate club moms journalism? Facebook journalism?), they did cite their sources. That's how much food from Fresh Direct costs. And it's in New York City where groceries can be more expensive* (often Fresh Direct is a decent price depending which neighborhood you live in). Potentially those of you with cheaper grocery prices could also get cheaper restaurant meals but I don't see anybody thinking of that. And the article even explains that they didn't comparison shop because the second, undefended, prong of their argument is that people don't have enough time to comparison shop.
I mean, yes, the article is ridiculous and is trying to be just stupid enough (but not too stupid) to engage people in the comments and get them to direct other people to it to "get a load of this". Step 3: profit! But I do know some people who try to make restaurant food at home so they buy expensive ingredients and then they don't have a plan for what to do with the remainder. I think the "cooking at home" gospel has been bandied about so much in popular personal finance that people don't understand any of the underpinnings of it and are then disappointed that they don't magically get rich from doing it.
*I am happy when I can get pasta or carrots on sale for .99/lb and even in the 5-pound bag lentils are over $1/lb.