Translation:Not fifty-two cities, but fifty-seven!
"kettő" and "két" are interchangeable. You can use any of them anywhere to say "two".
When you really want to make sure you are understood use "kettő", because "két" can be mistaken for "hét".
To elaborate a little bit on that one, there is one difference in usage. "Két" can not stand on its own. It has to be in a compound word, or it has to refer to something, a noun or something like that. For example, you can say "Két alma" - two apples. But you can not answer the question "How many apples is this?" with just "Két.". On the other hand, "kettő" can stand on its own. And it can replace "két" anywhere, but it is usually only done for clarity. Like the way the English would say "niner" for "nine".
So, the long form of "two" should be used in this sentence, perhaps as "model", in order to avoid using the short version of the Hungarian word for "two", which sounds like the word for "seven". . . . . thereby employing such emphasis in order to clarify any/the possible misunderstanding as to what is being said. Thank you! [I am such a critic!]