"That's the way it's supposed to be sung" is only justifiable as a comment one might make on hearing a particularly effective rendition, which might or might not be close to whatever the original version of the song might be.

Rather like the kind of compliment to give to a cook - "that's what I call a proper Shepherds Pie (or whatever)".

You'd need to be a kind of contortionist to pat yourself on the back like that fella...