It has some third party software like chrome, eclipse, ... etc. mostly development tools. I tried it without a usb drive attached, but same result. Here is the result of pmset:
tog-mac:~ jchun$ pmset -g assertions
2016-12-28 11:41:18 -0500
Assertion status system-wide:
BackgroundTask 0
ApplePushServiceTask 0
UserIsActive 1
PreventUserIdleDisplaySleep 0
PreventSystemSleep 0
ExternalMedia 0
PreventUserIdleSystemSleep 0
NetworkClientActive 0
Listed by owning process:
pid 98(hidd): [0x00001ace00098239] 01:48:27 UserIsActive named: "com.apple.iohideventsystem.queue.tickle.4294970413.17"
Timeout will fire in 895 secs Action=TimeoutActionRelease
Kernel Assertions: 0x4=USB
id=509 level=255 0x4=USB mod=12/31/69, 7:00 PM description=com.apple.usb.externaldevice.14800000 owner=Touchscreen
Idle sleep preventers: IODisplayWrangler