After the green apple splat meltdown, the workers were kept behind that one side door. After the students left behind went down that corridor, they didn't meet anyone but blue tasselworms. Up until this point, the only tasselworm we saw was the reddish-brown one with t green and yellow sweater. This means that the blue ones are at least different. Plus, the main tasselworm is amazingly sentient, if you are paying attention. Maybe he's even the missing principal!