As Will mentioned, what you're describing is a failure of object detection, assuming that the USPS logo is visible in the alerts that simply reported a "truck". (USPS detection works by recognizing the logo.)
If the logo is visible, please report the misclassified alerts as such to help us improve the recognition. How do you that varies a little depending on where you're viewing the alert...
In email you click the "please help Camect learn" link directly. From telegram, you'd click "thumbs down" and then "please help Camect learn". From the UI, you click "thumbs down", and then uncheck the box that says "the detected objects are correct" to be prompted to share the video clip. (These methods are mentioned on page 11 of the "Learning More about Camect" guide linked off
camect.com/welcome.)
The first time you share a clip you'll also have to go through the steps to enable Google drive if you have not done that already. It's a one-time thing and subsequent clip sharing will be much faster.
Lastly, you are correct in thinking that you should not thumbs down the "truck" (i.e. other than if you're following the above steps), or else Camect will start to think you don't want to be notified about trucks. We have discussed separating the reporting of incorrect detections from "thumbs down" in all modes of viewing to make this distinction clearer, and we may do that in future.