Bathroom door shook on its own in great-uncle's apartment

In 2015 some inexplicable shit happened to my great-uncle in his own apartment. He still tells this story in the smallest detail and swears it's all the honest truth (and crosses himself while doing it — he and grandma are hardcore believers, sometimes to the point of fanaticism).

Anyway, one morning grandma went off to the eye doctor, and grandpa decided to screw back on the handle of a cabinet that had fallen off the day before. Grandpa's sitting in the kitchen by the stove fiddling with the handle, the kitchen door is open, and right across from it there's another door — to the bathroom. And then at some point that door starts jerking, shaking, like someone is trying to break it down FROM the toilet. Even though nobody was turning the door handle, it was like someone was trying to smash the door itself in with their whole body. Grandpa nearly had a heart attack there. He says he stood in the middle of the kitchen, looking at this shit and not knowing what to do. Run out of the apartment? Well, that means running past the bathroom, scary. Jump out the kitchen window? Like hell, it's the sixth floor. Though the urge, according to grandpa, was definitely there. This shit lasted about a minute, then everything suddenly went quiet. Grandpa couldn't calm down for a long time, then he started saying prayers, mustered up the courage and opened the bathroom door. Naturally, there was nobody there and everything was in perfect order.

Grandpa insists it wasn't an auditory hallucination or anything like that — he clearly saw the door shaking and heard blows against it from the other side. I suggested that grandpa had gotten high on gas by the stove (you never know), but he swears there was no fucking way, because he thought of that himself and immediately checked whether there was a leak anywhere. In the end he and grandma decided it was all demonic stuff and invited a priest to bless the apartment. That's the kind of shit it was.