What does it mean for something to be an 'Art'? Does it just mean for someone to do creative things in the field of their work?

No, Einstein was doing science. He tested his imagination, he didn't just put into into a story or a picture. I'd count anything that attempts to communicate and realizes it's fiction as art.

Art is a means of expression. Just like words carry meaning, art carries ideas, emotions, feelings and the like. It does not matter what you conjure up from your imagination as it is not art unless it expresses something, unless it can stir something within the one who experiences that piece of art, unless it has meaning. Albert Einstein it a scientist. His theories were not imaginings, they were realities. He read reality and saw it through his imagination. He did not create a personal meaning in the form of art.

How art thou, flounder? Artifice is official and artificial is the old english for artistic. Noah's arcane alluvial plainly drains are into new verb of being, thus art was a state of static ideal, and science was the dynamic dumped overboard when gypsies escaped on balloons . A flair in handling the rigors of any discipline as if whimsy was leading the adept, has art immolated as a verbb and resurrected as the expression of one who is the science that just couldn't be quietude. In other architecture, the state of science was conveyed with articulating an arithmatic arterial in making artifacts of Aramaican references to B of A.

Art is a fuzzy and vague concept, and itf you use non standard logic than theres no worry saying (in one context) something that is definately not art, in another context, that it is. Or of something (even in the exact same context) that it both is and it is not.