Seriously, if I had to guess, I'd say it was someone shooting a low-budget film. The door was propped so that the equipment could be easily loaded in and out, and the old guy was probably crew. The mystery there would be why do it on the dates when your event was in town; it would make more sense to do it when rooms were cheaper. (Wouldn't necessarily be a skin flick; film students tend to like run-down hotels to create a certain sense of atmosphere.)
True story: Many years ago, DH was once an aspiring filmmaker, and he and his friends used to shoot location scenes without permits. On one occasion they decided to work on an action sequence that depicted someone being pushed off a cliff. They rigged the scene with a dummy and got it in one take -- which happened to be witnessed by someone who lived nearby. The witness called the state police; who started a manhunt for the murderer and sent boats onto the river to look for the dead man. Talk about having some 'splainin to do.