Is there a word for an explanation that is simple but wrong? [duplicate]

In an academic context (which the OP explained in a comment), the particular type of fallacy used is called a Red Herring. It is sometimes called the Chewbacca defense, after a South Park episode.

Red Herring

...the speaker deliberately brings up an irrelevant issue.

(Source: Thank you for Arguing, Jay Heinrichs, p. 149)

Chewbacca Defense

In a jury trial, a Chewbacca defense is a legal strategy in which a criminal defense lawyer tries to confuse the jury rather than refute the case of the prosecutor. It is an intentional distraction or obfuscation.

As a Chewbacca defense distracts and misleads, it is an example of a red herring. It is also an example of an irrelevant conclusion, a type of informal fallacy in which one making an argument fails to address the issue in question. Often an opposing counsel can legally object to such arguments by declaring them irrelevant, character evidence, or argumentative.

The name Chewbacca defense comes from "Chef Aid", an episode of the American animated series South Park. The episode, which premiered on October 7, 1998, satirizes the O. J. Simpson murder trial, particularly attorney Johnnie Cochran's closing argument for the defense. In the episode, Cochran bases his argument on a false premise about the 1983 film Return of the Jedi. He asks the jury why a Wookiee like Chewbacca would want to live on Endor with the much smaller Ewoks when "it does not make sense". He argues that if Chewbacca living on Endor does not make sense—and if even mentioning Chewbacca in the case does not make sense—then the jury must acquit.

(Source: https://en.wikipedia.org/wiki/Chewbacca_defense)

Specious is the word you're after. Another word that fits the bill is simplistic.

characterized by extreme and often misleading simplicity

a simplistic theory of the universe.

[Etymonline]