Updating Ubuntu - Simple/rookie question

Hey!

Every few days I update Ubuntu via ruing "Software Updater", at least that is what I though.

I just did so, and then I opened "Ubuntu Software". There are 3 updates there which did not get downloaded via "Software Updater".

Why is this the case? Why split updates to two places? Is there one way to update everything, instead of checking out two places?

The updates are: "OS Updates", "Archive Manager" and "Software & Updates".

Thank for any help!