For the unfamiliar, there is a subculture of urban exploration surrounding "draining", the act of exploring storm drains and (sometimes) sewers. It can be a fun adventure at times as many drains have large "features" such as massive underground rooms, historic brickwork, cave formations (e.g. stalactites), water storage tanks or waterfalls. Most of the time, they don't even smell that bad and you can get some cool photos. You also often will find oddly-shaped mushrooms growing out of the walls of the tunnels. This is most likely just some group of explorers who were not so careful to observe rule #2: don't be seen entering/exiting the drains. Rule #1 is "when it rains, no drains."
I’ve seen some videos of people who vacuum out sidewalk cracks in places like NYC. They find gold and jewels and such. Quite interesting what people can find. I’d bet the storm drain area has some nice spots for heavier material to accumulate.
In books, movies and videogames people spend a considerable amount of time in the sewers. In fact, I’m pretty sure they spend more time in the sewers that in standup meetings. Reality mirrors fiction. Speaking of which, some getting acquainted with sewers may be in order for the upcoming AI apocalypse.
I’m not sure if you are referencing the article but a witness made the same link:
> Speaking to NBC New York, witness Aki Jakupovic said: “Three random guys walking around in a strange suit, open the sewer, go in like Ninja Turtles.”