Tarmack
Rhetorical Porcupine
I don't see why he isn't free to make YouTube Channels as he please's maybe he might have a channel for IRL stuff and not wan't a machinima partnership what authority do they have to sue him just for making new channels.
Ask if he'll let you read his contract. Do a keyword search for "exclusive" and read the pieces. Most contracts specify exclusivity for the contract duration. It's a protective measure on the part of the company. Remember, he agreed to what is in the contract. Whether he understood it is irrelevant.
Now, it may be just non-competition in which case it would only prohibit channels of a type that compete with Machinima.
It's designed to stop someone from using Machinima to build up a nice subscriber base and then announce to their subscribers they're making a new channel, walking away with a new competing channel and a ton of subs for the deal. Perfectly valid and reasonable.