You can definitely add multiple widgets in the same row.
You can drag the new widget in the existing row at the end of the row or between existing columns and it will add a new column within the same row. If you hold the widget before dropping it you will see "Column" with blue background. Drop it there and it will add a new column within the row.
If you drag the new widget above the existing row it will display "Row" with blue background and if you drop there it will add a new Row.
If you drag the new widget above a column inside an existing row it will display "Inner Row" which will add a new Row within the column.