Cheat Map?

Hey, OK, so I was playing the 'living dead' playlist when I got talking to some guys. After a few more games we decided to play custom games. We played for a while on numerous maps and then this guy loaded one up. It was called 'BOTGROUND', and it was on High Grounds. We were going to play FFA Slayer, and i didn't know what the map was like. When we started I was shocked.
There were around 50 Elites and Spartans, with no weapons, just dormant. The guy described them as 'bots'. You could kill them and they would drop 4 grenades (Spartan-frag, Elite-sticky). They would then respawn after around 3 minutes.
The other thing was the objects. There were dozons of Oddballs and dozons of white flags all over. You could pick them up and kill with them, that was the idea. Oh and yeah, the main gates, they were down by the beach.
I have no idea how this was done. I'm pretty sure that it wasn't the guy i was playing with, i think he downloaded it.
I have heard of 'modded maps'. To be honest, i have no idea what these are or how they are done, just that strange things can happen.
Any advice would be much appreciated. I have the map still, but if it's not legit I don't want to keep it. I also have some screenshots here (i didn't want to embed them, this post is allready really long):

The flags and skulls.
http://s301.photobucket.com/albums/nn59/Snipers-Stealth/?action=view&current=FlageSkulls.jpg
The 'bots'. There are no player-controlled people in this.
http://s301.photobucket.com/albums/nn59/Snipers-Stealth/?action=view&current=CheatMapOv.jpg
Sorry for this long post. Again, any advice would be much appreciated. If you would like to see the map, please contact me. If you could tell me what this is, that too would be awesome.
Gamertag: Snipers Stealth
Thanks,
~SS