The Big Mac index started as a joke, but became a somewhat respectable—if still highly informal—way of measuring Purchasing Power Parity. Argentina took advantage of this by making it really cheap but hiding it so no one would order it, artificially improving the country’s score.
While your claim may or may not be true. The posted article doesn’t support it. It only says that the inflation according to BigMac is higher than official reporting numbers. There’s nothing on it supporting any government interference on the Hamburg price to lower the numbers.