By original do you mean the one in the database or the one on the device?
If the device spit out the same SHA3, then either it had the exact same image, or the SHA3 was planted somehow. The idea that it's actually a different file is not a reasonable doubt. It's too unlikely.
By the original, I mean the image that was used to produce the initial hash, which Google (rightly) claimed to be CSAM. Without some proof that an illicit image that has the same hash exists, I wouldn't accept a claim based on hash alone.
Oh definitely you need someone to examine the image that was put in the database to show it's CSAM, if the legal argument depends on that. But that's an entirely different question from whether the image on the device is that image.
If the device spit out the same SHA3, then either it had the exact same image, or the SHA3 was planted somehow. The idea that it's actually a different file is not a reasonable doubt. It's too unlikely.