I thought the same thing. It was a bit more subtle for me, but it prompted me to draw a sun, and when I first started drawing, it said "I see circle" but kept guessing, and with a few more lines it concluded, "I know, it's sun". Then a few drawings later I got circle, and in one second it said, "I know, it's circle".

At first I was thinking, how could it know this is a circle, but for the sun, it knew circle wasn't it when I had only drawn a circle. But it just occurred to me that the program probably tells it whether or not it's right before it actually verbalizes the guess/answer.

Then a few drawings after that, I got bus, and it guessed school-bus about 15 seconds in, and it wasn't until 10 seconds after that when it finally guessed just bus. So, I'm guessing this is the same for yours, it was simply guessing police car before car (probably because the NN takes probability into account and has gotten that as a right answer more often or something), and in your case it just happened to be right so it stopped guessing before it tried just "car."