It's true in the context of our idea about what we call the physical world, but really there's no way for you to find out the truth or reality of anything. Only through the help of knowledge passed down generation to generation do you experience anything.

So technically that statement is true, but actually it depends on what you mean by "sun", "ice cube", "close enough", and "melt".

One could argue the sun itself doesn't do anything to the ice cube. Do you define the sun as an entity that has heat separate from itself and applies it to the ice cube? Or is the sun itself heat? Etc....

What do you mean by ice cube? An ice cube 1000x the size of the sun will probably not melt.

What do you mean by close enough? An ice cube left out in the sun can melt on earth, but also the earth has huge ice caps that haven't melted. Etc

I think you get the point. For all intents and purposes that we would use, yes it is true. But it ain't necessarily so, or not objectively true without specific context. I think it was George Box that said "all models are wrong, but some are useful."

But at the same time the statement is false because an ice cube will likely sublimate in the vacuum of space before it came close enough to melt.