Cashier's check indicated a person with same last name of customer as the remitter.
Given the high likelihood that this is a counterfeit item, I would infer that the customer's last name was used to try to make the phantom remitter appear to be credible.
However, he indicated the money was from a church to be sent to Nigeria. Why would a church give him the money to send?
He has had several wires in/out with no clear explanation of the funds.
I agree with your conclusion that he's a mule. Maybe willing, maybe a victim.
In any case, I recommend that you put the brakes on the wire and look into the deposited item further before releasing any funds.