I prefer an aisle seat
Due to if I need to stretch my legs or spend a penny (but I think it's only Ryan Air that charge)
I hate having to disturb people if I need to get up as have had the aisle occupant sleeping in the past.

I think that you may be correct with the bad shoulder, as I have lost count of the amount of times I have been bashed with carry ons or the buy on board trolly etc

Strange behavior without saying anything

Could easily have just said, I hope that you don't mind if I sit here as I keep getting knocked in the aisle etc