Regardless if it is a sneak attack or not, Queen was a goner the moment Sanji found out Queen's actualy location while staying invisible.
Think about it, it is Sanji's credit that he found out where Queen is while Queen failed to find out Sanji is, the moment Sanji found Queen first and started his combo attack, the only outcome would be Queen getting blitz combo'ed simply because Sanji was too much faster than Queen.
TL;DR Sanji could discover and attack invisible Queen, while Queen was unable to react to "invisible" Sanji.