You don't know about the remaining 70 are true negatives or not, so you can't use that data for calculation. If you only consider the 930 cases where there is

You don't know about the remaining 70 are true negatives or not, so you can't use that data for calculation. If you only consider the 930 cases where there is verification, you do come up to 59% accuracy. Even using your generous assumption of the 70 cases being true negatives, the dog only come up to 62% accuracy.