He is a silver medalist in the sense that he wants to be the pirate king, and based on strength he should be weaker or equal to whitebeard but not stronger
This is just his bluff, we have the king saying the opposite regarding Whitebeard and Kaido and besides that Whitebeard is stronger than Roger the PK, being the king of pirates is one of the secondary goals for Kaido, just like any emperor , their lives don't end if they don't reach ONE PIECE,pirate paradise, rule the world, set the world on fire these are examples apart from Kaido's plans, one piece is nothing more than +1, build the biggest and strongest army in the world, cause the biggest war.