Dementor-like entity in the sky

My partner and I were talking about unexplained things we have encountered. And I thought his was interesting and wanted your thoughts.

Basically, he was in a park in Toronto where he was smoking weed with his friend back in 2012. They were both looking at the sky and then he noticed something that he describes looked like a “dementor from Harry Potter". He said it was very still in the sky with the clouds moving past it like they normally would on a grey windy and cloudy day. He said its robe moved with the wind but it remained still in the sky.

The creepy part is that his friend asked “hey! Do you see that thing in the sky?" before he could even say anything. To this day he feels creeped out about it.

I was thinking maybe it could be someone pulling one of those drone pranks, but I don’t know how good drone technology was back in 2012.