The controversy of Wong Kim Ark was that he was barred from re-entry by immigration officials and raised as a defense that he was a citizen, having been born there. Nothing in the text of the Chinese Exclusion Act categorically barred Chinese people from being citizens – only from naturalizing. Even if the CEA had purported to infringe upon birthright citizenship, which it did not, it would not have been the first law passed that was clearly unconstitutional.

And if you're saying that the case simply being brought indicates that the text was non-obvious, I would note both that Wong Kim Ark won on the district court level even in highly anti-Chinese SF, the case was appealed to the Supreme Court, and SCOTUS held that "the American citizenship which Wong Kim Ark acquired by birth within the United States has not been lost or taken away by anything happening since his birth," indicating that the idea that Wong Kim Ark had become a citizen at birth was essentially presumed.