Not quite, but close to correct.
Found sets (including the current record and current sort order) are specific to a given Table Occurrence in a given FileMaker window. Table Occurrences are the "boxes" found in Manage | Database | Relationships. Each refers to a table, but you can set up more than one such occurrence for the same table. Every layout specifies a single table occurrence in the "Show Records From" drop down found in Layout Setup and also in the New Layout Wizard.
So, for a given window, all layouts that specify the same table occurrence share the same found set, current record and sort order. A change to any of these will affect what records are displayed in all of the layouts that refer to the same table occurrence.
Script steps that modify the found set, current record or the sort order all execute in the context of the current layout. They will modify (or attempt to modify) the found set of whatever table occurrence is specified for that layout. This also will be specific to whatever FileMaker window is current.
And note that I keep referring to windows here. If you open a second window in FileMaker, you get a whole new and separate set of found sets for all of your table occurrences in this window. Changes to a found set will not affect the found set for any layout shown in a different window.