Probable reasons i might think of, why you see those DB's being backed up are:
You have an SQL Agent job scheduled somewhere to take those backups:
Either a Maintenance plan exist which is taking those backups.
May be there are AD-HOC backups being taken via SSMS:
This may be the reason you might be seeing those DB's getting backed up due to VSS (Volume Shadow copy service).
In order to check this, please run the query below from here to find how are you're DB's getting backed up.This will give you the application name which will help the cause on how these backups are occurring.
SET NOCOUNT ON;
--this version reads all trace files
declare @path nvarchar(100)
set @path = (select top 1 [path] from sys.traces where is_default = 1)
set @path = (select reverse(right(reverse(@path), (Len(@path) - (PATIndex('%[_]%', reverse(@path)))))) + '.trc')
SELECT STE.name AS EventClassName,
FROM sys.fn_trace_gettable((@path), DEFAULT) ST
INNER JOIN sys.trace_events STE ON ST.EventClass = STE.trace_event_id
WHERE TextData LIKE '%backup%' AND SPID <> @@SPID
ORDER BY StartTime DESC;