What is reported is not the number of successful recognitions, but the total number of scan requests the device sends to the server, regardless of whether it contained a (new) target or not. When using continuous cloud recognition, a new scan is sent at a fixed interval, as specified when calling CloudRecognitionService.StartContinuousRecognition (by default in the Unity sample the interval is 1.5).
From the Cloud Recognition documentation:
Scans Scans are in effect calls from the Wikitude SDK via the Client API to the Cloud Recognition servers. All commercial license come with an allowance of 1,000,000 scans per month per developer account. Note: When using Continuous Search mode multiple calls are made to the server.
Yes, when the app is minimized or when the phone is locked, the SDK is paused, the camera is stopped and no further scans should be made.