Question FTP. Explain, why is my drive can be operatable in sleep mode?

[ditrate]

I was able to create folder and close my FTP client (FIlezilla), while HDD was still in standby mode. All actions was made, and after that I heard that my drive begin to wake up.
Is this was request on delay or what?
My FTP: Router and WD My Book.

 

[lvt]

The sleep mode only stops the HDD's platter from spinning, everything else is still working. The platter would start spinning as soon as needed.

 

[ditrate]

The sleep mode only stops the HDD's platter from spinning, everything else is still working. The platter would start spinning as soon as needed.

Thank you, Wise Man.