Because "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo" is a grammatically correct sentence in American English, used as an example in linguistics.
That's what the paragraph "The buffalo from buffalo Who are buffaloed by the buffalo From buffalo Buffalo are the buffalo from buffalo" in the lyrics is referring to.
You'll notice the Wikipedia page actually refers this Alt-J song as a "use of the sentence in popular culture"...
To understand this song you need to know the verb "to buffalo", which is not very common (more like slang), it means "to bully" someone.
Also, check this Wikipedia page: en.wikipedia.org/wiki/Buffalo_buffalo_Buffalo_buffalo_buffalo_buffalo_Buffalo_buffalo
Because "Buffalo buffalo Buffalo buffalo buffalo buffalo Buffalo buffalo" is a grammatically correct sentence in American English, used as an example in linguistics.
That's what the paragraph "The buffalo from buffalo Who are buffaloed by the buffalo From buffalo Buffalo are the buffalo from buffalo" in the lyrics is referring to.
You'll notice the Wikipedia page actually refers this Alt-J song as a "use of the sentence in popular culture"...