For someone born in or around 1938 (actually earlier as the first 1938 stories depict him already as a past-teen age man) reading the story as re-written in 1986 is not particularly reliable.
In the original Kar-El was born on Krypton allright and sent to the Earth as a newborn.
And - whether he was actually born on Krypton or on the Earth - the Certificate of Birth is definitely false IF it states that Jonathan and Martha Kent are their parents, an on th eother hand actually adopting him wouldn't have been as easy as it may seem from the comics strips.
See also (for fun): http://thelegalgeeks.com/2016/06/18/how-did-ma-and-pa-kent-a...
In any case I would say that Superman's citizenship and actual legality of documents as Clark Kent are highly debatable, and I wouldn't be using that as an example for proving US citizenship.
https://en.wikipedia.org/wiki/Origin_of_Superman#Pre-Crisis
"In 1938, DC Comics published Superman's debut in Action Comics #1, Siegel and Shuster were required to cut the story down to thirteen pages, and so the origin story was reduced to a single page. The story described a scientist on an unnamed doomed planet placing his infant son into a hastily designed spaceship and launching it toward Earth. When the spaceship lands, a passing motorist finds it and turns the child over to a local orphanage"
"The first issue of Superman, published in 1939, also featured the origin story. Max Gaines had written to Siegel and Shuster and asked them to expand the origin sequence to two pages, and to include four pages that detailed how Clark Kent became a journalist as well as a full page feature that expanded on the scientific explanation for Superman's powers. In this issue, the passing motorists are revealed to be the Kents, who leave him at the local orphan asylum but later return to adopt him. "
etc.
I guess you are talking of the circa 1995 series:
https://en.wikipedia.org/wiki/Origin_of_Superman#Superman:_T...
first episode was titled "The Last Son of Krypton", not "Yet another baby from Kansas".
Let's leave that as a rhetorical question having nothing to do with TFA on BofA.
Anyway it is actually documented, here is the prologue from the first episode of the "Superman (1940s cartoons)":
https://en.wikipedia.org/wiki/Superman_(1941_film)#Prologue
“In the endless reaches of the universe, there once existed a planet known as Krypton; a planet that burned like a green star in the distant heavens. There, civilization was far advanced, and it brought forth a race of supermen, whose mental and physical powers were developed to the absolute peak of human perfection. But there came a day when giant quakes threatened to destroy Krypton forever. One of the planet’s leading scientists, sensing the approach of doom, placed his infant son in a small rocket ship and sent it hurtling in the direction of the Earth, just as Krypton exploded. The rocket sped through star-studded space, landing safely on Earth with its precious burden: Krypton’s sole survivor. A passing motorist found the uninjured child and took it to an orphanage. As the years went by and the child grew to maturity, he found himself possessed of amazing physical powers. Faster than a speeding bullet, more powerful than a locomotive, able to leap tall buildings in a single bound, the infant of Krypton is now the Man of Steel: SUPERMAN! To best be in a position to use his amazing powers in a never-ending battle for truth and justice, Superman has assumed the disguise of Clark Kent, mild-mannered reporter for a great metropolitan newspaper.”
At least, that was official origin in the comics starting with John Byrne's The Man of Steel in 1986 and for several decades afterward.
That version of the story also explains why he looks enough like the Kents to pass for their biological son: the birthing matrix is designed to shape the child to look like whoever removes him from it because only his parents are supposed to do that.