Yeah its pretty crazy how advanced its sound calibration is. It uses its microphones (six of them) to measure the response of the sound in the room according to where its placed, and adjusts itself on the fly so that it sounds as good as it does.
So if you pick up your homepod and move it in your room - say from in the middle of the table to near a wall, it will change its sound profile (after about half a minute) to lower bass and minimize reflective frequencies from the wall. Having an omnidirectional speaker blast into the wall would not sound good without that kinda calibration, as you would get reflective sounds from the wall and too much bass.
It does further calibration like this one put in a stereo pair to make sure _both_ homepods are outputting the best sound together.
The audiophile equivalent of this is getting a good mic, hook it up to your $5k stereo, and then use the manufacturer provided software to calibrate it. Then never move anything around your room again or hang new art of throw down a rug, because if you do that you have to recalibrate again.
The homepod is really some crazy audio engineering. One of apple patents describes some of stuff that probably went into the Homepod [1]. There is also a fun review [2] that was posted on the reddit audiophile back when the homepods first came out.
1 - http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=....
2 - https://www.reddit.com/r/audiophile/comments/7wwtqy/apple_ho...