You can't expect everyone's use of language to be impeccable. The two mean more or less the same, but the police have vehicles that aren't squad cars - unmarked high-performance cars, for example.
The article was saying that he stole a police car - and, to be more specific, it was an ordinary blue four- door sedan fitted and painted for everyday police use. But the journalist didn't have time to say all that. Most speakers of Br Eng would just say 'police car' anyway.
Student or Learner