It's misleading because Byrd renounced his beliefs. The NAACP says: "Senator Byrd reflects the transformative power of this nation. Senator Byrd went from being an active member of the KKK to a being a stalwart supporter of the Civil Rights Act, the Voting Rights Act and many other pieces of seminal legislation that advanced the civil rights and liberties of our country."

You didn't read the linked article, did you? Byrd changed his ways and was even praised by the NAACP for his capacity to change:

  “Senator Byrd reflects the transformative power of this
  nation,” read a statement by NAACP president Ben Jealous.
  “Senator Byrd went from being an active member of the KKK
  to a being a stalwart supporter of the Civil Rights Act,
  the Voting Rights Act and many other pieces of seminal
  legislation that advanced the civil rights and liberties of
  our country.”

It may not be false to say that Biden spoke at Byrd's funeral, but it's definitely misleading to call it hypocrisy.