snap and apt ( or deb's) are different packaging systems. Some software is nowadays only availabe as a snap-package but was distributed as deb-package in earlier days. To make the snap installable via apt, so called transitional deb-packages are used.
chromium-browser is such a transitional deb-package, when you install it, it will pull in the snap-package chromium.
When you remove the deb-package chromium-browser it will just remove the transitional deb-package but not the snap-package chromium, thus the application is not uninstalled and still functions properly, if you want to remove the snap you'd have to run snap remove chromium, not snap remove chromium-broser as you wrote in your question, a snap named chromium-broser or even chromium-browser simply does not exist.
~$ snap find chromium
Name Version Publisher Notes Summary
chromium 115.0.5790.102 canonical✓ - Chromium web browser, open-source version of Chrome
chromium-ffmpeg 0.1 canonical✓ - FFmpeg codecs (free and proprietary) for use by third-party browser snaps
...
...
...
~$ snap find chromium-broser
No matching snaps for "chromium-broser"
~$ snap find chromium-browser
No matching snaps for "chromium-browser"
~$ apt show chromium-browser | grep Description
WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
Description: Transitional package - chromium-browser -> chromium snap