I'm not even convinced the basic argument that a language with 40-odd million people regarding it as their primary language is not widely spoken is true (never mind the ludicrously false clickbaity "no-one speaks" headline). Sure, more Indonesians speak other languages at home and with fellow native speakers because they're the local languages of particular areas, some of which were more widely spoken than the Malay dialect Bahasa Indonesian was based on in the first place, or else closely identified with their ethnic and cultural backgrounds. And the fact that Bahasa Indonesia is the main language of domestic politics and education (and largely irrelevant outside Indonesia) means that people who speak the languages of their ancestors are bound to view speaking it instead of their local dialect as stuffy and formal regardless of its linguistic characteristics (see also: other multilingual countries) and bound to create slang versions that incorporate their local words which aren't particularly intelligible to foreigners schooled in the classroom version.

And I don't think even English, usually the sole language spoken by native speakers and definitely not lacking in standard phrases and vocabulary, would pass the author's litmus test of "do native speakers in different regions of England all speak it in everyday conversation in a manner so close to the textbooks a foreigner can easily understand it"