The difference between two MySQL delete user statements (delete user and drop user)

mysql 15:13:12>>create user yeyz@'%' identified by '123456';
Query OK, rows affected (. sec)
mysql 15:20:01>>grant select,create,update,delete on yeyz.yeyz to yeyz@'%';
Query OK, rows affected (. sec)
mysql 15:29:48>>GRANT USAGE ON yeyz.yeyz TO 'yeyz'@localhost IDENTIFIED BY '123456';
Query OK, rows affected (. sec)
[email protected]:(none) 15:20:39>>show grants for yeyz@'%';
+---------------------------------------------------------------------------------------------------------------------+
| Grants for yeyz@% |
+---------------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'yeyz'@'%' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9' |
| GRANT SELECT, UPDATE, DELETE, CREATE ON `yeyz`.`yeyz` TO 'yeyz'@'%' |
+---------------------------------------------------------------------------------------------------------------------+

mysql 15:20:43>>delete from mysql.user where user='yeyz';
Query OK, rows affected (. sec)

mysql 15:21:40>>select user,host from mysql.user;
+------------------+-----------------+
| user | host |
+------------------+-----------------+
| dba_yeyz | localhost |
| root | localhost |
| tkadmin | localhost |
+------------------+-----------------+
 rows in set (.sec)

mysql 15:24:21>>show grants for yeyz@'%';
+---------------------------------------------------------------------------------------------------------------------+
| Grants for yeyz@% |
+---------------------------------------------------------------------------------------------------------------------+
| GRANT USAGE ON *.* TO 'yeyz'@'%' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9' |
| GRANT SELECT, UPDATE, DELETE, CREATE ON `yeyz`.`yeyz` TO 'yeyz'@'%' |
+---------------------------------------------------------------------------------------------------------------------+
 rows in set (0.00 sec)

mysql ::>>GRANT USAGE ON yeyz.yeyz TO 'yeyz'@localhost IDENTIFIED BY '123456';
Query OK, rows affected (. sec)

[dba_mysql@tk-dba-mysql-stat-- ~]$ /usr/local/mysql/bin/mysql -uyeyz --socket=/data/mysql_4306/tmp/mysql.sock --port= -p -hlocalhost
Enter password: 
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 
Server version: 5.5.-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql--yeyz@localhost:(none) 15:31:05>>select * from yeyz.yeyz;
+------+
|id|
+------+
| 3 |
| 4 |
| 5 |
+------+
 rows in set (.sec)

mysql--yeyz@localhost:(none) 15:31:16>>delete from yeyz.yeyz where id=;
Query OK, row affected (. sec)

mysql--yeyz@localhost:(none) 15:31:32>>select * from yeyz.yeyz;
+------+
|id|
+------+
| 3 |
| 4 |
+------+
 rows in set (.sec)

mysql ::>>drop user yeyz@'%';
Query OK, rows affected (0.00 sec)
mysql ::>>drop user yeyz@'localhost';
Query OK, rows affected (0.00 sec)
mysql ::>>
mysql ::>>show grants for yeyz@'%';
ERROR (): There is no such grant defined for user 'yeyz' on host '%'
mysql ::>>show grants for yeyz@'localhost';
ERROR (): There is no such grant defined for user 'yeyz' on host '192.168.18.%'

mysql ::>>GRANT SELECT ON *.* TO 'yeyz'@'localhost' IDENTIFIED BY PASSWORD '*6BB4837EB74329105EE4568DDA7DC67ED2CA2AD9';
Query OK, rows affected (. sec)

[dba_mysql@tk-dba-mysql-stat-10-104 ~]$ /usr/local/mysql/bin/mysql -uyeyz --socket=/data/mysql_4306/tmp/mysql.sock --port=4306 -p -hlocalhost
Enter password: 
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 
Server version: 5.5.19-log MySQL Community Server (GPL)

Copyright (c) , , Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql ::>>select * from yeyz.yeyz;
+------+
|id|
+------+
| |
| |
| |
+------+
 rows in set (0.00 sec)

mysql ::>>update yeyz.yeyz set id= where id=;
ERROR (): UPDATE command denied to user 'yeyz'@'localhost' for table 'yeyz'
mysql ::>>create table test (id int);
ERROR (D000): No database selected
mysql ::>>create table yeyz.test (id int);
ERROR (): CREATE command denied to user 'yeyz'@'localhost' for table 'test'