Someone might want to message the mods of whatever subreddit he was banned from. I don't know enough about the situation to feel justified in doing so. But I checked /r/spam, and found this:

http://www.reddit.com/r/spam/comments/2g5k5k/overview_for_db...

Couple of very high karma users who sound like domain experts vouched for him.

That said, it doesn't look like he was shadowbanned sitewide. Most likely an automoderator action. I can still click on his user profile.

Edit: unrelated, but how do you generate a submission history for a user? I'm a mod of a smaller sub, that looks like a useful tool.