How did my databases shrink?
You can use the Power of Default Trace to find out the culprit.

provided the default trace files are not rolled over

-- find out the default trace location



SELECT * 
FROM fn_trace_getinfo(default);
GO

   --- check the events

SELECT 
    TextData,
    HostName,
    ApplicationName,
    LoginName, 
    StartTime  
FROM 
[fn_trace_gettable]('Location of Tracefile.trc', DEFAULT) 
WHERE TextData LIKE '%SHRINKFILE%';