I would be surprised if this were true, and reluctant to take a single poster's vague assertion as confirmation that it happens. It could just as easily have been that person's misunderstanding about which terminal they were supposed to arrive at.

Airlines have a real incentive not to do this. For example, whether you can make a tight connection at LHR can depend critically on which terminal you arrive at. That's why there's such a plethora of MCTs listed for different combinations. Airlines aren't going to randomly deposit people in the wrong terminal and make them miss their connections when the airlines will then be on the hook for all the consequent costs (possibly including 261/2004 compensation).