The auction itself only says the cuffs, which are gaffed for quick release, could have been used for "underwater escapes." However, a press release put out by the auction house on December 2 featured speculation that "the rare pair was probably for use in his particularly risky Chinese Water Torture," and the idea caught fire, especially in the Daily Mail which went as far as to report that the cuffs were a "vital prop" in Houdini's most famous escape.
However, it's well documented in photos and reviews of the time that Houdini did not wear handcuffs in the Chinese Water Torture Cell.
The gaffed handcuffs [Lot 47] belonged to the late Billy McComb and are among a selection of 260 lots of conjuring books and magic memorabilia on sale this Thursday, December 12. The cuffs are accompanied by a letter from McComb detailing how he acquired them from Douglas Geoffrey (aka Hardeen Jr.). The handcuffs and letter are estimated at £2,000-3,000.
UPDATE: The cuffs sold for £2300.