where a hard drive can appear as a USB drive when setting up wireless networking. I believe this is what happened on your computer.
I think ComboFix detected the file because one of the files it calls (setupSNK.exe) is also a name used by some malware. This, with the fact that it’s unusual to have autorun.inf on a hard drive, makes it look suspicious.
You could probably just delete it as its serving no purpose.