Thanks for sharing your experience, it is very strange to get the decision made early and still hold you to complete the 12 months period, most of people complete Exam Invitation to Oath Ceremony in period of 3 months.I do not think so, he just got test invite pretty quickly that'sit. Pretty sure if he calls them they will robotically remind him about 1 year processing time. I have completed my test on September 10 next day - decision was made, during the interview the officer told me to expect to receive an oath sometime in February/ March.
I do not think his case is abnormal - but do not think calling will help, however he can still call just to be on safe side