The point being here is that this is not a zero sum game; there are many benefits to growing stuff other than producing food.
A lot of the vegetables grown in Dutch greenhouses mentioned in the article are actually exported; though other countries are starting to do the same now.
This area here is the most well known and largest greenhouse area in the Netherlands (and probably world wide). It's comparatively tiny (about 100 square KM). https://www.google.com/maps/@51.986133,4.233423,25389m/data=... https://www.jpl.nasa.gov/spaceimages/details.php?id=PIA21986
The reason greenhouses are used there is because they produce way more per square meter than traditional farms can. That and access to cheap gas decades ago caused a boom in greenhouses to happen. Currently many of these greenhouses are switching from gas to clean energy. Over the last 4-5 decades, local farmers have optimized their production and they now run very efficiently.
The Netherlands is (by far) the largest exporter of tomatoes world wide. Most of those are grown in these and similar facilities as well as many other crops (i.e. this is not dedicated to just tomatoes). It's a vastly more efficient way to use land. The point here is that it doesn't take much space to feed a city.
For example, fresh herbs cost a fortune in grocery stores here, and are festooned with single-use plastic packaging, and come in far larger quantities than one can reasonably use before they go bad. So it makes tons of sense to have a little herb garden in your house or yard, especially if you can grow things that are adapted to your local climate (e.g. my rosemary bush is taller than I am).
But I think the optimal scale inside of expensive cities is probably closer to "houseplants that you can eat" rather than an urban farm.
If you live in a high-cost city, the best thing to grow in your backyard from an environmental standpoint is probably an ADU (backyard cottage for someone to live in), and the best thing to grow in your spare bedroom is probably a roommate. Displacing walking-distance housing to do farming is a huge loser from a climate perspective.
Of course there is more to life than emitting as little CO2 as possible, but to the extent that urban farming has environmental benefits, it is in exploiting niches caused by shitty land use decisions in the past and present.
(By way of illustration, the average car commuting 20 miles each way every weekday for a year emits 4.6 metric tons of CO2, so according to the article you could grow and transport something like four and a half tons of greens for the same carbon footprint. Maybe I'm weird but that's a lot more than I go through in a year.)