I was looking at the SM firmware on Github and noticed that in the configuration file the default filament size is 3.00mm (see below).
Out of interest why has it been set to 3.00mm? I checked the same file on the Marlin repo and it defaults to 1.75mm which means SM team has intentionally changed it.
This is the default setting in Marlin firmware code and the firmware developer did not change it. Snapmaker does not have the filament width sensor, so this diameter does not matter.