Why does Milinda step into Nagasena's trap?

Referring to the discussion between Milinda and Nagasena: Why King Milinda does not consider all together - pole, axle, wheels etc. - his chariot? Normally one defines a chariot a means for transportation consisting of pole, axle, wheels, etc. This would be the correct answer to Nagasena's question what the chariot is. Instead, when pressed by Nagasena he names *chariot* only *a designation, a description, an appellation, a name*. That is, Milinda rejects the correct answer. Now Nagasena has an easy time to defend the Buddhist principle of anatman.