Well, if you had reason to believe that the police placed a bomb then it makes sense to me that you might not trust whoever you get on the other end of the line when trying to contact a bomb squad.
In fairness, while it was in a garage, it was not on a car.
"We saw no other option but to use our bomb robot and place a device on its extension for it to detonate where the suspect was," Dallas Police Chief David Brown told a news conference Friday. "Other options would have exposed our officers to grave danger. The suspect is deceased as a result of detonating the bomb."
https://www.npr.org/sections/thetwo-way/2016/07/08/485262777...
To me it would only be reasonable to suspect a bomb on one's car if one did not know that the police placed it there.