The fact they were working at CMU suggests they were already paying them market value.
The fact they aren't working there anymore suggest they weren't.
Depends on your definition of market value. If they went to multiple companies I'd say CMU was paying below, but the fact they all went to Uber suggests that Uber paid well above market value to make sure they accepted the offers.
What I think actually happened is that Uber treated the Robotics Engineering Center as a startup with a set of internal working relationships and expertise that they wanted. Since they couldn't actually buy the Center they just hired away all the researchers.
So the employees rather than shareholders, managers or the CEO got a fat paycheck for being good at their jobs. That's communism!
I'm not saying it's necessarily a bad thing but it's different from how we usually evaluate market value for employees.