That is the literal fable of the sour grapes. Foxy can't reach the grapes, they are too high up and out of his ability to attain, so he says they're sour. So, yes, it is sour grapes. You can now be sure.
The story wasn't about the morality of whoever put the grapes out of reach of the hungry. I'm confident that's wrong too. But the story was about the hungry person's reaction.
This was actually a common tale of my childhood, I forget some of these old tales are no longer shared and certain phrases remain in the language as a sort of fossil...
Wikipedia is often wrong but they're right about this. Any public or school library probably has a reference copy of Aesop's Fables if you prefer to see in the flesh.