Whatever voodoo they are pulling out of thin air, is clearly not present on commodity, non-tuned Btrfs filesystems. That, and most people have backups set up on their NAS.
Well, if you want, you can just pull the drives out of your Synology box and hook them up to any Linux system [1]. So whichever way they're tuning it, it can't be that voodoo-esque.
[1] https://kb.synology.com/en-global/DSM/tutorial/How_can_I_rec...