Hello!
I believe something caught a small-scale fire, that's most likely. Then again, we don't know what kind of 3D printer this was - might be that it used some kind of chemicals that emit carbon monoxide while polymerizing or something like that.
That's the thing with 3D printers - they are pretty slow with the process, it's not uncommon to see printing times in range of many tens of hours. So it's tempting to start a printing job and go to sleep. And this can be dangerous. If you're awake and you start feeleing bad, you have a chance to open the windows, go outside, do something. If something like that catches you when you're sleeping - it's much more dangerous. We should use it as warning and pay more attention ourselves.
Thanks for reading
Paweł