The first small problem with the Reuters article is that the usual spelling for the language is ‘Pirahã’, with a tilde over the final /a/, indicating that the vowel is nasalized .
I myself must confess to saying obstinant, inordinant and indiscriminant, with nasalization from the preceding nasal misinterpreted as belonging to the suffix.
The reason that there is no "ng’ sound is that this alphabet treats that nasal consonant as a feature of the vowel - not a separate nasal consonant, but a vowel produced with nasalization .
In speech, hard ‘r’ frequently gets nasalized , in the same way as ‘k’ becomes aspirated in the American throat.
In southern England, the vowel is nasalized and long.
But after, for example, verbs ending in ‘a’, ‘en’ gloms onto the verb and turns the final ‘a’ into an ‘eh’ sound, creating a long, nasalized ‘eh’.
Try saying ‘cromps,’ while nasalizing the m a little, like in French.
French is essentially a language that elides everything that doesn't get out of the way fast enough, and nasalises everything else.
Also, the nasal cavity can be closed thus preventing vowels from being nasalised and thus increasing their comprehensibility.
All Albanians north of the Shkumbin, along with the Albanians of Montenegro, Kosovo, and most of Macedonia, speak Gheg dialects with their characteristic nasalization .