More likely a bug than a drophack.
The hacker would have to somehow get your IP, which he can't get from League of Legends. You are never directly connected to someone else, so no one ever has the chance to get your IP from League.
Though, if you clicked a link or something from anyone during the game, your IP would be visible to the owner of the website it leads to.
I have seen someone post a link to a what appears to be a known website, but a single character may have been swapped and the link actually leads to someones private website. From there, the one who posted the link can obtain the IP of the one who clicked it, thus allowing for drophacks (unless the reciever has some DDoS protection).