Partial Source: The Wrestling Observer

As seen Sunday night at Survivor Series, Mark Henry returned to action by answering Ryback's open challenge, and defeating him. According to sources, the short-lived storyline was copied from TNA Wrestling. On iMPACT! Wrestling on Spike TV, former WWE Diva and reigning TNA Women's Champion Gail Kim has been issuing open challenges, which inspired WWE's creative department to utilize the idea for themselves.

For what it's worth, this is nothing new. WWE and TNA have used each others ideas for years now.