I wouldn't say it automatically qualifies as suspicious activity, but because this is not a typical transaction for this customer, I do think it qualifies for further review. Who was the money order payable to, and how was it used? Also, if you 314(b) (yes, "314(b)" is now a verb), I suggest contacting the institution that took the MO for deposit to see if there is any unusual activity on the other end.
If, after reviewing all of the facts, the transaction still appears to be suspicious, then file.