Good guess. Communist professors (who have abounded at Columbia since the 1930's) tend to set up "cell" classes that are somewhat sealed off from the "G-pop" (to lapse into wardenspeak), so that indoctrination can proceed with somewhat enhanced security and more candor in the classroom. This became part of the public record when Houston-area media looked into the granting of tenure to a bonafide Marxist-Leninist professor who had a "cell class" that he was leading in an atmosphere of cultic navel-gazing.
Remember, Columbia is where Barky met Bill Ayers. If their class entertained jolly stories of pipe-bombings and murder from the Good Old Days in candid exchanges of comradely gemuetlichkeit, then that group will not exactly have been meeting with open classroom doors. In short, whoever was running that part of the syllabus, whoever was on Obama's committee, was running a Communist student cell.
That's why Obama was so low-profile at Columbia, IMHO.
The episode with the dubious tenure grant occurred at a small college named College of the Mainland in Texas City, Texas (an exurb of Houston and Galveston on Galveston Bay). Several Texas FReepers FReeped the tenure grant, sending e-mails to the dean of the college and to local media and political leaders (Republican congressmen and state legislators). The tenure grant went forward anyway.