It's strange how those with Christ hadn't at that point, casted out demons and this man [whoever he was] was already doing it.
I looked at other Bible translations and it appears the reason the disciples "forbad him" was because he wasn't in Christ's group. But then Christ opposed them, saying- "forbid him not" indicating that he who isn't against us- is with us.
And I wonder- though he wasn't hanging around with the disciples, it "could be" that he was a follower of Christ none the less. Remember in the O.T. when one of the prophets thought he was the only follower of God left and God told him that there were at least 7000 [i'm guessing] more?
Well, maybe that man was a follower of Christ- but other than what the disciples reported, the scriptures are silent in regards to who he was?
Another thing that is interesting, is that some will cast out demons in His name, Yet Christ will deny them; proving that even people who are able to do this- as so many in the ministry claim- don't necessarily have their hearts right with God.
So back to this man- he was either casting out demons with a proper heart, or he wasn't. But I know- that still doesn't tell us very much does it?