The test's popularity lies in its ability to translate the complex language of psychiatry into childhood images we all know. It’s much easier for people to relate their anxiety to Piglet or melancholy to Eeyore than to study dry medical manuals.
Yes, and that's perfectly normal. The human psyche is complex; in different situations, we might exhibit Piglet's anxiety, Rabbit's fixations, or Tigger's hyperactivity. The test shows which of these archetypes is currently dominant or most prominent in your personality.
Scientifically, the test is semi-humorous and cannot be used for a medical diagnosis. However, it is based on real DSM criteria, so it can accurately highlight certain personality traits or emotional tendencies that might deserve attention.