You stated that they cannot pronounce the sound because it doesn't exist in their language. That is completely different than implying they thought it was spelled with "Rs" all along.
Besides, a quick check in a dictionary will tell you that the word PIRROW doesn't exist.
It's a misspelling dude, based on the way the pronounce the word obviously. That's it. Not that big of a deal and not funny unress you rike making lacist jokes against Asians.