Then why didn't they just come out and say it? To me it seems like they must have had Kota express his doubts for a reason. There are also some other suspicious clues:
1. Vader is constantly lying and deceiving. In the first game he changed his story every time they met.
2. Memory is not stored in DNA.
3. The "distant thunder body" from the challenges is not wearing the robes that Marek died in.
4. The novelization for the first game may have been written before the second game was planned. Star Wars has been known to contradict itself in its sequels.
But that is a pretty good reason to argue that he is a clone. Thank you.
To me, cloning is just a gimmick to resurrect an old storyline. Clone or not, the plot for this game was pretty weak. What with all of the flashbacks strewn everywhere it seems more like the sentimental reunion episode of a sitcom than the sequel of a motion picture. When Kota said that the fate of the entire rebellion rested on the battle of Kamino I was really disinclined to believe him. The storyline went from being great to "remembering the good old days" in the blink of an eye. That's why I hate clones.