I don't think it is called that. The name "Hempel's Opening" seems to have been added to the WP article for the opening as a hoax.
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I fully understand why it is called the Saragossa here is the wiki entry about it -
This opening became popular in the Saragossa chess club (Zaragoza, Spain) in 1919. The next year club member José Juncosa analyzed the opening in Revista del Club Argentino.[1] In 1922 a theme tournament requiring the players to open with 1.c3 was arranged in Mannheim with three participants, Siegbert Tarrasch, Paul Leonhardt and Jacques Mieses, which Tarrasch won.
However Hempel's Opening is nowhere to be found, there was a child prodigy called Jutta Hempel but she to my knowledge never once played that opening and I've been looking online in forums and on old pictures for a while now. I would really like to know how it got two names...

If anyone knows why you will be my new knowledge/chess hero!