It's mostly straight on the opposite side and the perpendicular sides. Could be but going with most likely based on what info is available.
To do that it'd have to be stored on some sort of fulcrum I'd think...lol
Yeah, I bought mine from a guy who had it sitting on a shelf for who knows how long, with the front half hanging over the edge. The bowing is probably more pronounced on the right-hand side of the machine because that's where all the heavy stuff is - drive chassis and PSU.
If there's damage to the top case in that area as well, that would suggest UPS damage. Otherwise, I think it's just physics and time that are to blame

EDIT: One thing you can do to test is pop out the motherboard. If it returns to a flat shape, then you're probably looking at acute UPS damage. If it stays bowed, it's probably long-term warping.