This is an idiom and can't be translated directly. Spanish uses "que" and not "como". Think about it this way: does "how" make literal sense in English? It is just an exclamation you learned as a child, but is literally meaningless. If it did mean something, one would reply to the "how"... but you can't. In that respect, so is "que". Just something to memorize ;) English has other idioms like this, such as "how are you?" Again, the how is meaningless because you do not answer the "how" you answer "what you feel."
Qué is used in front of nouns, adjectives, and adverbs to say how or what.
Cómo is used before conjugated verbs and means how.
Cuán is used before phrases that begin with an adjective or adverb and are followed by a verb phrase. It means how.
Cuánto is used in front of nouns and verb phrases and means how, how much, how many, what, etc.
Could "¡Qué interesante!" also be translated as "That's interesting!"? In reading DL discussions, I find I frequently say to myself, "That's interesting!" rather than "How interesting!" If my my response could be correct, I will report it.