I informed him that the proper term actually is "fantastic", and that it was one of those words that has changed meanings over time.
I notice that every word that conveys a positive attitude gets diluted over time. Something used to be as if from a fantasy to be fantastic. Now it just means very good. The same is true for words like "awesome", which used to mean something that stupefied you in amazement (and "amazing" is another such word).
I suppose it is nice to have so many different ways to express positive feelings, but it also is a shame to lose their original meanings. After all, without "fantastic", we don't have an adjective for "fantasy".