That's right. There are a lot of generations of motors over the years from Lego. I've got a lot of them. Mindstorms alone, between late 90s and now, had three major types. Pre-mindstorms there were the 4.5v motors and the 9v system. A number of different shapes too. Then there are all the ones that combined some form of controller with motors, such as Cybermaster and the Star Wars Droid Developer / Dark Side sets.
In the midst of all that, Lego have been updating their Power Functions motorised system and I think the latest one is compatible with the latest Mindstorms (51515). Getting the Liebherr 9800 means I've probably got a lot of those now too.