You seek to understand the CSIDL values that show in the ATP reports correlated from SEP detections on local clients.
This is a known issue that affects the SEP clients. It is resolved in SEP 12.1.6 MP5
In SEP versions prior to 12.1.6 MP5, system variables that Microsoft uses are exposed in the event sent to ATP. Please update your SEP clients and SEPM servers to 12.1.6 MP5 or later to resolve this error.
These variables are similar to other variables that are more common such as %temp% and %windir%. Here is Microsoft's reference page for these values: