Yes, this is understood. They could have been drawn into the case to that extent only, without pressing any charges.
MIT was involved collaterally as the scene of the crime, and ceased to be involved after JSTOR and the Feds took over.
So JSTOR had a case to withdraw. Their involvement was not limited to being the target of Swartz's actions--they played an active role, only to withdraw later.
But I could be mistaken and my reading of Lessig could be wrong. How did JSTOR take over? How did it come to pass that JSTOR dropped its case? What was its case? Could filing such a case count as "being drawn in" to a case?