Reporting overall doesn't really do anything. Only way you can really be detected is by VAC or UAC, but most hacks out there that if you bought em are protected by that specific threat. He found out your IP by either DoSing you or using a program called MW3sa. This program is a partner with Force Host, what it does, gives you a list of the players name, steam_id and IP addresses and allows you to disconnect players from your game.
Alot of people abuse this program. They will either disconnect you because you do infact hack, or feel threatened by you cause you actually some skill in that game, so they wanna disconnect you anyways. I know that second reason first hand