How to detect reason why motherboard fry

I just bought my Macbook Air 3 months ago. This Wednesday, I’m using it normally in the evening. Next morning, I turned it on and after about 10 minutes, it suddenly turned off. The Apple engineer said my motherboard, chip, and display connector is fried and tell me it cost about 1500$ to repair. He said it must because I spilled water on it, but I really didn’t. I use it very carefully and didn’t spill any water on it.

Is there anyway to tell if this is damaged by water or by other reasons? I really didn’t split any water on it.