After reading the linked article, it got me interested enough to find a paper [1] as one of the top hits suggesting that it's not a pidgin:

Pasting for convenience (paragraphing added for readability):

> Related to the two previous claims, it is occasionally suggested that Riau Indonesian might be a pidgin. Since one of the hallmarks of a pidgin is a radically reduced grammar, such suggestions are generally motivated by my characterization of Riau Indonesian as having a very simple grammar.

> Be that as it may, Riau Indonesian fails to meet the profile of a typical pidgin on multiple other grounds.

> Structurally, pidgins generally also have a small lexicon, but that of Riau Indonesian is in the same ballpark as those of most other languages. Moreover, pidgins are typically unstable, exhibiting lots of variation, whereas Riau Indonesian, as argued in Section 2.7 above, is as stable as any other language.

> Sociolinguistically, pidgins lack native speakers, whereas Riau Indonesian, as observed in Section 2.4 above, has lots. In addition, pidgins are typically used in a limited set of communicative contexts, whereas Riau Indonesian, as noted above, is used in a wide range of contexts.

> So for these reasons, at least, Riau Indonesian is clearly not a pidgin.

[1] https://sastra.um.ac.id/wp-content/uploads/2010/01/PU-David-...