I received several changeset comments from members of the Grab team. They have a standard wording:

Of course, data can become outdated - some of the changesets were 5 years old. Newer imagery can show more details, etc.

But in my impression, the mebers of the Grab team just fail to see the difference between “residential” and other minor road types. True, many “residential” classifications currently on the map are wrong.

Just look at the images in the general wiki on highway: https://wiki.openstreetmap.org/wiki/Key%3Ahighway
A “residential” is lined with houses, while on an “unclassified” there may be a house here or there, but long sections without houses are normal.

That becomes clear also from other wiki pages:
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dresidential
https://wiki.openstreetmap.org/wiki/Tag:highway%3Dunclassified
https://wiki.openstreetmap.org/wiki/Malaysian_Roads_Tagging

I request Grab member to learn that.
If they then happen to find a way which requires a different tagging because they have newer imagery or preferably ground truth, just change the classification, without any comment.