Well I've read several articles that say it's a commen misconception that Lisa had pre-emtive multitasking, like the one linked below under "Notes":
It is a common misconception that the Lisa OS used preemptive multitasking.
but to be honest, does it really matter? Many computers were putting up firsts back in those days and they all fed off one anothers ideas. They're all golden age machines and did their bit at improving the market as a whole.