In a movie, there is an expression which I can not understand. The situation is like the following.
There are two men, A and B, driving in a car and calling a third person over a mobile's speakerphone.
A: I don't want to listen to him (the third person) anymore.
(A throws the mobile phone out though a window)
B: That was mine.
I don't understand why B says "That was mine."
This sentence has past tense. Even though A throws the phone out, does the phone still belong to B?
So it is natural that B should express his opinion by using present tense, isn't it?