Bitaddress isn't truly random. It is based on the seed (your mouse movement), which isn't random.
Its a PRNG[1] and as such considered random enough for cryptographic purposes.
Human movement always follows some pattern or purpose. Mouse movement is no different. In fact, in some ways, nothing is random. "Randomness" is the misconception of not being able to define the answer because we do not have the means to.
Randomness is defined as the lack of pattern, we as humans are essentially pattern matching and recognition machines. Just think about all the people that see the face of Elvis in vegetables. If we are unable to see a pattern we call it random. This lack of pattern is what protects a randomly generated key. IF there would be a pattern between the first and the next key you generated it would be possible to derive one from the other. Since you cant its perfectly fine to call it random, unless you want to start a philosophical debate.
[1]
https://en.wikipedia.org/wiki/Pseudorandom_number_generator
