D’OH!
You’re right. See, what I said about “wild guesses and personal fan fictions” also applies to me. I was so excited by the finding that I didn’t pay attention to what Ryoredcyclone was saying AT ALL, thus ending up making a HUGE mistake. I’m sorry. 
Yes, Ryoredcyclone was pointing out that Capcom typed ハマブランカ Hamaburanka wrong in the quiz. That’s why they were so amused, because even Maja blanca DOES exist (so even with a typo Capcom ended up referencing something real, LOL). Ryoredcyclone added the post to a previous one where he complained about another typo (they had spelt the name of the muay thai champ before Sagat wrong, “Anukan” instead of “Nuakan”).
Thus the original was HAMA BLANCA. My bad. The origin of “Hama Blanca” is even more depressing than a Filipino dessert: HAMA Blanca was a leisure facility in Shirahama, Wakayama Prefecture, that closed in 2005.
(the photo was taken before 2015, as now there’s just an empty lot with only the plants left)
It had a large rainforest garden, a cactus garden, a flower garden and a rollercoaster. It was built to represent the epitome of a tropical paradise.
The origin of the building’s name was… you guessed it, CASABLANCA. Fused with the Japanese 浜
hama “beach”, because 白浜
SHIRAhama is “WHITE beach”. Therefore, “blanca”.
The fact that “Hamaburanka” comes from this leisure park ISN’T confirmed by Capcom, as Ryoredcyclone rightly points out; but come on, it’s so obvious to be almost in-your-face.
And that’s it as for Blanka’s name origin EXTRA universe. Then Capcom had to justify it IN universe…
…And that’s one of the two explanations I knew about, that even the Japanese Wikipedia page about Blanka does mention. The part you quoted, however, doesn’t have the note “* Japanese mispronunciation of ‘Hombre blanco’”". Wasn’t it there in the original? The Japanese Wiki doesn’t mention its source, so I don’t want it to be a translator guess.
It came from the SF2 Fanbook:

6: The secret of his name
7: The sound of a sneeze made by the beast who found him: “Blanka!”. Apparently, the young Jimmy (his real name) thought that it was his name.
8: B… BURANKA!
Yes, it’s ridiculous.
Yes, it’s more or less the same but doesn’t say “Brazilian natives”; only “When he began his life in the jungle, he was named ‘Blanka’ (which means ‘white’ in Spanish) because he was so fair-skinned”.
TL;DR:
- Blanka was named Hamablanka during development (confirmed).
- The name came from a leisure park in Shirahama (UNconfirmed, mine and Ryoredcyclone’s guess, even if it’s obvious).
- Capcom mistakenly wrote “Mahaburanka” in the quiz, and I mistakenly thought it was Blanka’s original name coming from a dessert (my mistake, it’s HAMAburanka=Hamablanca);
- IN-universe, Blanka’s name origin has had various interpretations:
1- The sound of a sneeze of the beast who found the young Blanka in the jungle (SF2 movie memorial fanbook); yes, it’s ridiculous but it was official;
2- Blanka was so named by the locals because he was still pale before becoming green-skinned, so “blanka” in Spanish… It would be blanco in correct Spanish, and even then, Brazil’s official language is Portuguese, where it would be branco. Anyway, it’s official nonetheless (Eternal Challenge);
3- Blanka was named “Hama blanka” because it was a mispronunciation of “hombre blanco”. This justifies his original name, and it was included in Complete File Street Fighter II. This is still not completely verified: the scan I’ve seen doesn’t include the note explaining that it was a mispronunciation of “hombre blanco”.
Phew! Thanks @Lord_Vega for the correction.