'folder-hook . set sort=threads' and 'set sort=threads'

[Zhengquan Zhang <zhang.zhengquan@xxxxxxxxx>]

Dear mutt community:

This has puzzling me for quite a while,
I saw in several muttrcs 

they use 

folder-hook .  set sort=threads

but I don't understand why they don't use

set sort=threads 

instead.

Basically they do the same thing. Is there anything I am missing here?

Thanks and Regards,

-- 
Zhengquan