Your general gist is correct: languages with CV (consonant-vowel) phonotactics[1] with a simple vowel systems tend to develop similar features, possibly through convergent evolution:
- agglutinative syntax (i.e. combining long sequences of words and suffixes to form complex meanings)
- vowel harmony (seems to exist in the earliest attested forms of Old Japanese, but not anymore)
- palatalization before front vowels (i, e)
- further simplification of the vowel system
My only nitpick is that Bantu languages are not relevant here. The author is explicitly focusing on Nigerian languages (although he titled that "Japanese words and name sound African"... Africa is a big continent with just as much language diversity as Asia, if not more). While there are some Bantu languages in Nigeria, they aren't as prominent there as they are in East, Central and South Africa. The author mentions Yoruba, Igbo, Fula, Hausa, Edo and several others - none of them is a Bantu language, although some are related. Even though you can put all of the languages above (except for Hausa) into the hypothetical Niger-Congo macro-family, together with the Bantu languages, they are quite far away by this point.
The other issue is that Bantu languages are probably not the best example for "Japanese-sounding" languages. They feature very frequent use of prenasalized consonants. While prenasalization almost certainly existed in Old Japanese[2] and is still retained in some northeastern dialects, this is not something people would identify with "Japanese-sounding" nowadays. Not to mention southern Bantu languages like Zulu and Xhosa that feature heavy usage of click consonants - these are completely alien to Japanese phonology.
But this doesn't detract at all from your argument. Languages with similar structure, will often sound similar. I think the other anecdote the author mentions (Plateau State languages sounding Sino-Tiban) also checks out. I am not familiar with any of these languages, but it seems many of them are tonal and based around heavy use of complex monosyllabic morphemes with complex combinations of initial consonant + medial glides(?) + diphthongs + final consonants. This is exactly what so strongly distinguishes the phonology and phonotactics of Sino-Tibetan languages.
[1] https://en.wikipedia.org/wiki/Phonotactics
[2] https://en.wikipedia.org/wiki/Rendaku#Origin