It's just one of the few differences in mechanics we had to adapt to in Australia when we switched from CCA mechanics (which we'd been using for over 20 years, so it was quite a challenge for me to break some old habits) to the IFAF (written by BAFRA) mechanics). James: when I worked games in Germany (Frankfurt), it seemed that the (German) mechanics manual was a translation of the IFAF/BAFRA mechanics, although my German is not good enough to know if there were any subtle differences.
FWIW, the IFAF/BAFRA mechanics only have SJ moving to the double umpire for a FG/PAT from inside the 5, outside that, SJ stays on their sideline, at the goal line to cover fake FG attempts.