You see, I might be a little biased here, but as we don't have the email in front of us I'm going to have to take a guess.
I'm fairly confident that was was meant by that was exposure in the form of his poem getting put into Minecraft, not exposure in the form of a shout-out or other promotion.
Unless the author releases the email we'll never know the context, but I've been a spectator to these types of negotiations enough that I strongly believe the context would support my interpretation.
