Well, North and south are
absolute directions, in that there is a North and South Pole, and the amount of "northness"
of an object may be defined by its proximity to that pole.
East and West, however, are
relative directions - as there isn't any "East pole" you have to define your reference point before you can label something as being "East" of that point. The 180° line of longitude (i.e. pretty much what the "date line" is) isn't accepted as a definition of "East"!
As your freind asked "What are the most Northerly, Easterly, Westerly and Southerly states in the US?" - then he has defined his reference point in the original qestion - the United States. The most Easterly State, by any conventional definition, is that State the most to the East of the Majority of the land mass, without travelling around the planet to get there.
Under your freind's definition, you travel East from New York and you eventually get to the Aleutian Islands, but travel
further East and you get to California, or Texas or wherever.