Fearless Tower
Touchdown! Greaser!
Even if his rating wasn't single pilot, there is no requirement for the SIC to hold a type rating as long as the airplane is flown in the US.500/550 series Citations can be flown single pilot with a single pilot waiver, pretty standard stuff. Lots of I's and II's are flown by one pilot, it does require either a commercial or ATP ticket, a second class medical and a check ride, but it's pretty common.
I flew a 551 so my type rating is CE500, not single pilot.