Solution to this is right there in the Editor Preferences. Inside Loading & Saving category, there is a property named "Load Level at Startup". By default, it's value is equal to Project Default. This means it will open a map defined as "Editor Startup Map" in project's settings under Maps & Modes category. We can change the "Load Level at Startup" value to either:
None - the editor will always open an empty map after boot up
Last Opened - the editor will always open last opened level
