Gearbox breakdown

My vehicle have been towed in to the dealer and the feed back was not up to standard as they told me that i wont be covered as the course of the problem is external influence and because of that my car will not be covered by the warranty, when i asked them how possible is it for the external influence can affect the gearbox. they couldn't give me the answer to that. They saying i have spill the liquid from the cup holder and it went through to the gearbox.