>  I have a question: how a link was added into my site 
> mirroring ? (Info: 	engine: transfer-status: link 
> added: www......). 

Probably because this was the default behaviour 
(follow "siblings")

> Is there an easy way to prevent that 

Yes : Set Options / Scan rules
And then, define exacly what you want:
-* +www.yoursite.com/whatever/*