Actually it's offset to PORT, (that's the other starboard
It's not that unusual.. it has it's advantages, pulling the shaft is one - on many boats the rudder has to be removed. On a previous boat of ours the rudder stock was off plumb my 2 or 3 degrees and it drove me nuts to look at it until I realized that that way the propshaft slid by the rudder cleanly.
It may also avoid excessive propwash torque on the rudder under power, which can be tiring on well balanced rudders.
Bob Perry did the same on his Mirage 33.. mayhaps he'll drop in here and explain the whys of it for us. C&C did it on the Ontario 32 as well.. so not uncommon. Lots of old wooden boats avoided drilling through the deadwood in a similar fashion.