The solution is a 32 characters long plain-text (the private key).
As far as I know, there is no 32 character private key. A
mini private key would have 30 characters.
I can only guess he means it is a brainwallet mnemonic. Don't mind giving additional hints, I've given up guessing... A couple parts that threw me was the anagram of Satoshi Nakamoto and the fact that it ends with ".txt"...
"WhyTheCombOfNatashaOtomoskiHas21" itself is 32 characters long and consists of 8 words... Hmm...