Here’s an extremely easy one. When in doubt, just knock on the goddamned door and talk with someone instead of kicking the door in, tossing flash-bangs and jamming rifles in people’s faces. Knock… and talk. SWAT shouldn’t be entering unless there’s a barricaded suspect.
The first thing is what they did. They knocked on the door, they spoke. At one point he was detained when they had a look about and then they apologised and left.
There was no SWAT (this is Germany so technically it would be a SEK team I guess), there was no flashbangs (why would police even have those?), there were no rifles in faces.