Zeus, in classical mythical fashion, took a liking to Hipolyta and got her preggers with Diana.
So why have the clay origin in the movie at all? The New 52 used the clay origins as a means of dispelling the idea that Diana is Zues' daughter, where as here it's known to everyone that Zeus is responsible for her creation, clay or not. If Diana and the rest of the Amazons know that Zeus was responsible for her creation, what's the point of using the clay origin as a means of deception when it doesn't even hide the important part? And again, where in the film does it hint that Hippolyta had an infatuation with Zeus? That was kind of a big deal in the New52's HIppolyta where Brian "She controls the men in her life" Azzerallo actually wrote that she and Zeus really had a thing going on. Like, he liked her more than Hera. In this movie, we get nothing but an acknowledgement that Zeus brought Diana to life.
Besides, making Diana a demi-god ala Heracles opens things up to the possibility-
Stop. No it does not. For DECADES, Wonder Woman has always dealt with the Gods in many ways without the writers ever having to resort to her being an illegitimate child of theirs. In fact, before New52, there was already a demi-god child of Zeus in the Wonder Woman comics. It was Wonder Girl, Wonder Woman's frequent sidekick! You're taking away Wonder Woman's unique origin and replacing it with her gawddang sidekick's origin! At least Bruce Wayne being part of a Circus would make more sense than Wonder Woman being a demi-god.
Oh, and that vague part in the Amazon backstory where Hippolyta freed the Amazons? The one responsible for their enslavement was Hercules himself. Changing it up so Hercules and Diana are siblings is just all kinds of wrong. And yes, there is a story where Wonder Woman and Hercules deal with each other and it's a good one. And they didn't need to be siblings in order to tell it!
Please tell me you're not going to explain to me the great story possibilities of having the Amazons be these man-murdering, child slavery endorsing idiots who can't even make their own weapons and armor. Not even the writers who worked on New52 Wonder Woman after Brian left could make it work. It wasn't until Greg Rucka did the write thing by eliminating all that junk and bringing Diana back to where she belonged.