Oracle SQL Plan operation INDEX FULL SCAN feeding into FIRST ROW

create table tq84_tab (
   num    integer      not null,
   txt    varchar2(3)  not null,
   val    number(4,1)  not null
);


create index tq84_tab_ix on tq84_tab(num, txt);


insert into tq84_tab
select
   mod(level, 100),
   dbms_random.string('U', 3),
   dbms_random.value(1, 999)
from
   dual connect by level <= 10000;


begin
   dbms_stats.gather_table_stats(user, 'tq84_tab');
end;
/


explain plan for
select
   max(num)
from
   tq84_tab
where
   txt = 'QUG'
;

select * from table(dbms_xplan.display(format=>'basic'));
--
-- ---------------------------------------------------
-- | Id  | Operation                   | Name        |
-- ---------------------------------------------------
-- |   0 | SELECT STATEMENT            |             |
-- |   1 |  SORT AGGREGATE             |             |
-- |   2 |   FIRST ROW                 |             |
-- |   3 |    INDEX FULL SCAN (MIN/MAX)| TQ84_TAB_IX |
-- ---------------------------------------------------

drop table tq84_tab;