I'd say it's a pretty common arrangement. Main guns tend to be right arm, secondary position would be the torso. Most people are right handed, making it a natural choice if not mounting paired main guns. Spreading out the weapons load means you don't lose everything if the right side gets hit hard, and medium lasers are the go-to secondary weapon across the board.
Some other examples (of the not Capellan-centric variety)
Clint - doesn't have missiles, but main gun RA, secondary MLs.
P-Hawk - same.
Centurion - AC10 RA, LRM10 LT, 2 MLs.
T-Bolt - LL RA, LRM15 RT (an anomaly, the SRM is in the left), 3 MLs.
Orion - AC10 RT, both missile racks on the left, 2 MLs.
Victor - AC20 RA, SRM4 LT, 2 MLs.
Battlemaster - PPC RA, SRM6 LT, 6 MLs.
Cyclops - AC20 RT, LRM10 LT, 2 MLs.
Atlas - AC20 RT, LRM20 LT, 4 MLs.
There are only so many ways for things to be laid out, it shouldn't be a surprise to see patterns form across designs.