Here is an ABC News report on the FBI's statement on the UC Merced attack. It is important to note that the statement says that the FBI had no earlier intelligence regarding Faisal Mohammad.
"At first, investigators said Mohammad wasn't connected to a terrorist group and acted in anger. But on Tuesday the FBI pulled back on details and the suspect's motive became unclear. Now the FBI isn't saying why they can't talk about the investigation."
I may be proven wrong as facts continue to come out, but if that young man had an image of an ISIS flag in his pocket as reported-but not yet confirmed by law enforcement- my opinion is that this was a case of lone wolf jihad.