How to remove vent assembly from Kenmore 665.16262400 dishwasher
Photos would definitely confirm but I believe your Kenmore is manufactured by Whirlpool and has an "open vent" style vent that is not electrically activated. From your description it seems that you already figured out to remove the top 6 T-15 torx screws on the upper inside of the door panel and lower the control panel to reveal the rectangular outer portion of the vent. 

If you shine a flashlight into the rectangular "throat" of the outer vent piece you will see how the round inner piece interlocks with it. Your intuition is correct, this two piece assembly simply unlocks and locks together when you rotate the round inner vent piece. If it is stuck you might spray the rim of the inner piece with a penetrating lube and use a hand towel to improve your grip upon it. Wipe off the spray lube afterwards to prevent any damage to the plastic. It is supposed to be tight because both pieces have a rubber seal which prevents water intrusion.