The gun taken from the police officer is not the correct type as used by Victoria Police. As of 2010, Victoria Police were armed with .40 calibre Smith & Wesson M & P (military and police) semi-automatic pistols.
If Carl was identified as the person making the bomb threat, he would be arrested and charged by the police, not just warned off and released into his mother's care.
Although the film is set in the streets of central Melbourne, Carlton and Parkville, there is no coherence to the sequence. The chase jumps from one part of the city to another.
It is unlikely that there would have been no calls to police and no response after Carl kills the students in their flat. The gunshots would have been heard by someone nearby.
When Carl calls in the bomb threat, he says the bomb is "under the examination room at the uni". Given the number of universities in Melbourne and the number of examination venues, this is very vague and it would be expected that the person on the other end would be asking for more detail.
Carl shows the bouncer his driver's licence with "82" on the back. This is his year of birth. Carl is supposed to celebrating his 21st birthday, but the film is set in 2012, making Carl 30.