What you heard is likely a reference to novelties that GMs research and keep under their hats until a major tournament. These are new lines, or lines the current book knowledge might indicate are inferior (but for which the GM may have a new variation calling that into question).
It's not so much an issue of playing incongruent openings, but rather experimenting with me ideas within existing openings.
Someone told me that when grandmasters play each other they don't play off the book they make moves differently. Let's say GM 1 plays the ruy lopez but plays it differently by making a different move and GM 2 master plays the stienitz defense (just an example), how can a person do that by making a different move without making a blunder? Can this be true or no?