Why do we love music? (2018)
pmc.ncbi.nlm.nih.gov
pmc.ncbi.nlm.nih.gov
Specific reasons for gibbon song rather than others:
1) duh, they are apes
2) unlike birds and cetaceans, but like humans, gibbons try to aim for a pure tone when singing, with energy concentrated at the fundamental frequency
3) unlike birds and cetaceans, but like humans, gibbons try to harmonize when singing in groups
You have not proven that this is the primary function of all music, ergo the article is not proven wrong.
In fact, I'd bet $100USD that the development of music was primarily for pleasure, not communication.