VMAC was a joint work by Wei Dai and Ted Krovetz. It so happens that Wei Dai at that time was also actively working on his own cryptographic library (Crypto++), which of course also includes VMAC.
You can find the test vectors here and the optimized implementation here.
Two examples for VMAC-AES-128 are:
A security definition is stronger if we make it easier for the attacker to win. The point being that the stronger definition rules out even this easier way of winning
In the specific case noted in the question, you are indeed correct.
The scenario you describe is the following:
An attacker queries "Cat" and receives the tag "90". It then computes the tag "...