Does sin befall me, and is my oath considered a false oath (yamin ghamus), after I clicked on the option "I swear by Allah that this is the original version" while downloading a disc that my son bought, and it turned out to be non-original, especially since I have doubts whether I knew this before downloading or after?

What you have done by purchasing pirated software is forbidden (haram) and requires repentance, unless you only realized it was a non-original copy after clicking on it; in that case, there is no sin upon you. As for your question about bearing the distributor's mistakes, the answer is that you are assisting him in sin and transgression, and Allah Almighty says: "And do not cooperate in sin and aggression" (Quran 5:2).