If the personal address of a streamer is publicly known, then there is a considerable chance malicious people try to swat them. Risk increases with viewership, which makes this instance rather rare. They call or email the local police department there and paint some urgent emergency, either the streamer has "taken a hostage", committed violence or whatever other serious crime thats necessery to provoke a response by the special commando of the police. In the USA thats often SWAT, which is where the name comes from. In Germany(like the video) the SEK would be the group to respond. Large streamers try their utmost to keep their location private, but most also have proactive contact with their local law enforcement, warning them about potential swatting attempts.

In reply to @helium1:matrix.org
https://old.reddit.com/r/linux/comments/1fg630o/rene_reb%C3%A9_a_well_known_linux_maintainer_and/

This happened after René was overly critical of the Rust kernel developers in a recent stream. A lot of commenters on YouTube are speculating that it was someone from the Rust community.

Lol, wild theory