The social expression “The same to you” is, of course, a polite reply by a greeted person to a wish or greeting that’s also applicable to the one who made the greeting at the first instance. When the greeting is “Have a nice day!” or “Have an enjoyable evening!”, it’s perfectly acceptable to reply “The same to you!” or “You, too!” But when the wish or greeting applies specifically and uniquely only to the person being greeted, as “Happy birthday to you!” to a birthday celebrator, the expression “The same to you” is obviously off-tangent and terribly inappropriate. The most common and suitable response to a birthday greeting is, of course, “Thank you!” or “Thank you very much!” The president of your country was therefore ill-advised in using “The same to you” to respond to his birthday well-wishers.