It could be understood that way, but I would say it's slightly incorrect. Mind you, I made the mistake too and being native and breezing through the exercises. :)
You would ask something like "Mikä eläin Mirri on" to ask about the species. Or "Minkä rotuinen kissa Mirri on" to ask about the breed of a cat that Mirri is.
However, "millainen" or "minkälainen" often refers to the classification of something, or calls for adjectives describing it.
Consider these two examples:
a) Mikä auto sinulla on? = What car do you have? You would answer this question with something like "Porsche Cayenne".
b) Minkälainen/millainen auto sinulla on? = What kind of a car do you have? / What is your car like? You could answer this with the category of a car, like "a sports car", or adjectives like "blue and fast".