It doesn't. What made you think it did? Are you sure you intended to ask what you did ask?

I notice that you have tagged this question with "aliens" as well as "UFOs", but I cannot think why, unless you are pulling someone's leg.

As Jon implies, in a normal fridge, in normal circumstances, within normal boundaries, everything will balance out to the same temperature. There may be a slight variation between the top and the bottom of the storage space, but apart from that you'd have to invoke the UFO theory.

I suspect plastic containers for carbonated drinks are made stronger (and therefore thicker) than for still water, due to the higher pressure of the contents.

Subjectively, therefore, a container of soda water picked up might not feel so cold to the touch because the packaging is a slightly better insulator. And it might also not cool as quickly for the same reason.

However, if enough time is allowed to reach stability, and the temperatures of the fluids themselves are measured by instrument, and they were on the same level in the fridge, then they have to be equal. Otherwise, you got yourself a perpetual source of energy.