I highly doubt it. Considering it was his grandfather's car and Jelani was close with his family, I don't see why he'd choose to abandon the car like that.
Is it possible he set it up deliberately so people would think he had been carjacked/killed? I suppose, but it doesn't sound in his character at all to do that. Sounds like he was really close with his family (at least his mom), and he hasn't had a history of running away or anything similar to this situation, so just leaving without a peep or by setting up a fake abduction/murder is improbable.
Also, speaking from my own experience in grad school, it usually doesn't start off super stressfully. There's ample time to freak/burn out later, but typically in the first few weeks of grad school, I'd say it's less stressful than undergrad. ISU's fall semester started on Aug 16, but
this article says that "Aug 24th was his first day of graduate school." Whether it was his first day or 2nd week, I can't imagine him already getting academically overloaded in such a short timeframe.
And I'm sure the meeting he had with his advisor was just a routine first meeting -- nothing negative.
Could he have been so stressed that he couldn't even bear to attend his first day of classes? Again, possibly, but my gut instinct says no. I think the majority of people are excited and optimistic on their first day of grad school. According to his family, Jelani had no history of mental illness. Could he have been hiding crippling anxiety? All the (albeit limited) info we have points to no. And from the surveillance footage, he looks put together, nicely dressed, and not like someone frozen with anxiety who was poised to run away from his life.