Wrong result for row comparison of trigger NEW/OLD: NEW = OLD returns 1 after a column change, OLD = (1,2,3) returns 0

CREATE TABLE t1 (a INT, b INT, c INT);

INSERT INTO t1 VALUES (1,2,3);

CREATE TRIGGER t1_bu BEFORE UPDATE ON t1 FOR EACH ROW  SET @r = CONCAT_WS(',', NEW = OLD, OLD = (1,2,3));

UPDATE t1 SET b = 20;

SELECT @r;   -- got 1,0   expected 0,1

13.2.0-dbg>CREATE TABLE t1 (a INT, b INT, c INT);

Query OK, 0 rows affected (0.009 sec)

13.2.0-dbg>INSERT INTO t1 VALUES (1,2,3);

Query OK, 1 row affected (0.001 sec)

13.2.0-dbg>CREATE TRIGGER t1_bu BEFORE UPDATE ON t1 FOR EACH ROW SET @r = CONCAT_WS(',', NEW = OLD, OLD = (1,2,3));

Query OK, 0 rows affected (0.006 sec)

13.2.0-dbg>UPDATE t1 SET b = 20;

Query OK, 1 row affected (0.003 sec)

Rows matched: 1  Changed: 1  Warnings: 0

13.2.0-dbg>SELECT @r;           

+------+

| @r   |

+------+

| 1,0  |

+------+

1 row in set (0.000 sec)

13.2.0-dbg>