Translation:Is it cold?
If you're referring to its use in a different question, it may have been part of the negative form, e.g. さむくない
For me the very previous question was: さむくないですか (Unless I'm remembering wrong) where さむく was just introduced as 'cold' so it threw me for a second.
Replacing the i of an i-adjective by a ku makes it an adverb. Samuku = "coldly".
What is the difference between this and つめたい? Is the latter only used for food/objects?
Absolutely right about つめたい meaning cold to the touch and さむい having to do with the weather, or ones perception of the temperature outside or in a room, however, it is つめたい that is used figuratively to mean cold hearted or unfeeling.
Is this also what you'd say if you were asking someone if they were cold or is さむい just for weather?
Usually in English, it would just be for the weather. In Japanese, it will mean both. Especially topics or questions regarding the weather or local climate, the culture is such that they are commonly used to:
genuinely talk about the weather
open up conversations [ anyone including strangers ]
ask about listener's well being
distract the listener away from present topic and talk about something else
Something to take note when interacting with a Japanese when it comes to weather