This is an old story, but in the 3rd printing of MW, he was made a soldier. Last I looked the Database still had the original version, not showing him as a soldier.
But trust me, he's a soldier.
There is an entire thread dedicated to this argument somewhere, and Ladinfance, chimed in saying that he is in fact a soldier.
That's interesting. Perhaps this should be updated in the database or spell book builder, or at least in the Rules and Codex Supplement or something. Then it wouldn't just be "something everyone on the forums knows but that isn't written anywhere." Using the "but Laddinfance said so" argument might not work everywhere without some evidence to back it up.
In the 3rd printing the card has been changed. The Arena printing should also have the corrected Sentry. I had made a document that collected all of the Errata into one place, but after I had made it, I'm not sure where it had gotten stored. Obviously, it is not on the Resources and Downloads page right now. Over the weekend, I'll rebuild it. That way there can be an easy way to have all of the current wordings for spells at your fingertips.
As for the Rules and Codex Supplement, I'm working on a bigger update to that, and it's still going to take a little while. Thank you for pointing this one out though, I had thought it was already in there, but I was wrong.
I hope this helps. I know how stubborn people can get if they don't see the evidence in the correct format.
If you have other questions, please let me know. I'm happy to try and answer them.