As Sir Tom sang - it's not unusual...
You will get different results from Motion Detection, Line Crossing and Intrusion Detection.
For best results ensure you're using 'VCA by Camera' in the setup as it's thought to be better than using the NVRs own VCA engine. With Motion Detection you only get an option to adjust the sensitivity and you can set it all of the way down to 0 (default is usually 60 or 80).
Line Crossing and Intrusion Detection have additional parameters such as the minimum/maximum size. You could set. the minimum to be larger than the cat. After setting the camera up via the NVR interface, you can log into the camera directly via Virtual Host and set the 'Target Validity' from Basic to High, Higher or Highest. There's also in the newer camera firmware 'False Alarm Filtering' that can be adjusted.
if motion detection is giving false alerts even when set to 'Human' and with sensitivity at 0, you'll have to experiment with line crossing or intrusion detection. When attempting to filter out false alerts work with one setting at a time.