Explicit ROW definition does not allow rows with one member.
But anchored definitions using ROW TYPE OF (or using %ROWTYPE with sql_type=ORACLE) do allow creation of rows with a single member.

Such variables fail to compare:

CREATE OR REPLACE TABLE t1 (a INT);

INSERT INTO t1 VALUES (1);

DELIMITER $$

BEGIN NOT ATOMIC

  DECLARE v1 ROW TYPE OF t1;

  SELECT * FROM t1 INTO v1;

  SELECT v1=v1;

END;

$$

ERROR 1241 (21000): Operand should contain 1 column(s)

The expected result is to perform comparison like it's done for rows with two or more elements.