Yes, it's a plug door - here's a nice photo, and it looks like just about the entire door mechanism is exposed, including what I assume is the air cylinder at the bottom. Shouldn't be too difficult to figure out what is restricting the opening
Jeremy
PS - Yes, it's a cute bus. The T809's wheels are noticeably smaller than the wheels on the T800 though, so I'm not sure that it's just a shorter wheelbase version