Yes, it’s true. I was tipped to this by ActuaLitté who has an article about it in French. Here’s the Google translation of part of it:
Oh it was fine, though kindly, mocked the whole world by announcing on April 1 arrival of books in 3 D. .. and one could believe in running gag on the part of Google Books, if the announcement was not followed by something much more serious.
Indeed, on the blog Inside Google Books, we find indeed an example of what could be the book homothetic in 3D, with a version of Treasure Island. (See the book 3Disé in full at this address).