The FDA announced 16 brands, typically higher end lines advertising grain free foods, may be linked to dilated cardiomyopathy (DCM) in canines. As I am not a vet or a scientist, I am not completely sure I am parsing the announcement correctly. Nevertheless, my impression is that their statement states the food itself is not bad or dangerous, rather that feeding dogs this food exclusively may not be a complete diet for a dog and lead to DCM. Is this assessment correct?
The announcement means they have found a correlation between DCM and dogs eating these types of foods. A correlation means simply that these two things tend to occur together, but it doesn't say anything about why or how.
"Between January 1, 2014 and April 30, 2019, the FDA received 524 reports of involving 560 dogs and 14 cats diagnosed with DCM. The FDA additionally received many reports of non-DCM cardiac disease in dogs and cats during this timeframe. To better understand the reported cardiac diseases, FDA investigated many of the DCM cases, as well as some of these non-DCM cardiac cases, by reviewing medical records and performing dietary and environmental exposure interviews."
This means the FDA reached the conclusion there was some correlation after receiving many reports, and doing an investigation into these reports to try to rule out other environmental factors. It would take actual experimentation, or medical studies to actually discern why such a correlation is occurring.
As your original article states, it's not even known exactly what the cause of DCM is, so no conclusion can be made at this time why this is so.
This announcement is meant to be taken as a warning that this food MIGHT be a cause of DCM, but it also might not be. If that worries you, then do not feed your dogs the foods in the list.
I will also note that "grain-free" is something of a recent fad diet for pets. Dogs and cats are known to be carnivores, and so people think feeding them grain is automatically bad, and advertising has picked up in this. The truth is food for dogs and cats, especially dry food, need some ingredients other than meat in order to bind the food together, and possibly to help getting the exact right balance of nutrition. Grain-free foods therefore contain other ingredients as a replacement for grains such as legumes or potatoes, which I'll point out is also counter to what people think dogs and cats should be eating. Although any of these foods could actually be being consumed by dogs and cats on a natural diet of prey animals, as these foods will possibly be in the stomach of the animals they eat. The FDA study simply shows grain-free foods are new enough that it isn't entirely known what kind of effect they have on pets.
In conclusion, while it cannot be said if grain-free is bad for pets, it's not necessarily better for pets either.