According to knowyourmeme the dude in the meme is a neanderthal character from a movie.
“Unga bunga” was originally used in a cartoon in 1950 with a caricature of an Aboriginal Australian, and it’s completely reasonable for someone to not know that. I didn’t until you prompted me to go and research the meme.
The phrase seems to be nonsense babble - there’s no way to deduce the Aboriginal Australian racism link from the movie image or caption, you have to actually research the backstory.