Other mistake: Throughout the film, you can frequently see many people's faces blurred, phone numbers blurred, store-fronts blurred, etc. This is because the production could not afford the rights to show these people, places and things, and simply blurred them out.
Continuity mistake: It is mentioned in dialog that during the last bird attack (the first film), a red rain was visible that seemed to drive the birds mad. However, at no time during the original film is there any red rain visible.
Trivia: Director James Nguyen was greatly inspired by the film "Sunset Boulevard", and thus includes several on-the-nose references to the film throughout. This includes a close-up shot of the sign for the actual "Sunset Boulevard" and including a key scene where a dead character falls face into a pool and is seen floating about, dead.
Trivia: In the opening scene, as Bill is being seated by Gloria, if you look closely you can see a copy of the script for the film in the background on a table. They were going over lines and someone set it down forgot to remove it from the shot before filming the take, but because it's slightly out of focus in the background and none of the words on it are visible, they didn't both going back to reshoot the scene. Just something funny to look for.