I cannot answer from a developer's perspective but from a Local SEO perspective I may be about to state "old news". Facebook's mobile platform has Nearby Places which is essentially a local search except that it takes place in Facebook and not on a browser. So having a GMB listing is not a prerequisite for a local business to be found in Facebook's local search.
Instead, the local business needs to be categorised correctly in Facebook and it may be that the headline is referring to the number of businesses that are correctly categorised?
When you use Nearby Places it is clear that it is aimed at the hospitality sector but it works anywhere where you could "check in" using Facebook. So it can work for any local business and I certainly advise my clients to take advantage of it as more and more people use Facebook on their mobile devices as their interface with the world.
From my experience (I am sure a lot of people know more about this than me) you need to set the business as a Local Business (there can be sub-categories) before you can "check-in". You can test this by searching for your business rather than category in Nearby Places and if it doesn't appear then tweak the categories. Then check-in or get someone else to do so. The more check-ins you get the better you will rank.
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