You might be right! Cassie said she knew the driver and starting sharing details about her roommate after the run-in with the inhuman driver. OP never explicitly said that they were the same person.

I don't think the tall boy took Cassie's roommate. She became a inhuman Uber driver right? Where is the connection between this creature and ride sharing?

Im guessing she was taken by a car-related inhuman. Cassie found tall boy, just one of many random creatures on campus, because she was looking for something in the rain.

If you got a posthumous degree, does that still count as graduating?