pg_stat_database update stats_reset only by pg_stat_reset

pg_stat_reset_single_table_counters/pg_stat_reset_single_function_counters
only update pg_stat_database column stats_reset.
stat_reset shuld update when all the column is reset.

sample:
drop database if exists lzzhang_db;
create database lzzhang_db;
\c lzzhang_db

create table lzzhang_tab(id int);
insert into lzzhang_tab values(1);
insert into lzzhang_tab values(1);

select tup_fetched, stats_reset from pg_stat_database where
datname='lzzhang_db';
select pg_sleep(1);

select pg_stat_reset_single_table_counters('lzzhang_tab'::regclass::oid);
select tup_fetched, stats_reset from pg_stat_database where
datname='lzzhang_db';

result:
tup_fetched | stats_reset
-------------+-------------------------------
514 | 2019-05-12 03:22:55.702753+08
(1 row)
tup_fetched | stats_reset
-------------+-------------------------------
710 | 2019-05-12 03:22:56.729336+08
(1 row)
tup_fetched is not reset but stats_reset is reset.