It is claimed that "every HTML table in Drupal 8 is responsive." What this actually means is that tables in the Drupal 8 admin UI are responsive and also that in Views, if you select a Table format, you have the opportunity to prioritize columns that will hide upon reaching narrower breakpoints. The strategy that is employed is that of adding "priority" classes to table cells and a "responsive-enabled" class to the table tag. At a tablet breakpoint, the "priority-low" table columns will hide and at the mobile breakpoint, the "priority-medium" columns will also not display.