Why EXISTS statement works differently in delete and update query?

Please tell me what am I missing with EXISTS statement. I'm following this website. https://www.geeksforgeeks.org/sql-exists/

I have two tables. Customers and Orders.

and here is delete query.

DELETE 
FROM Orders
WHERE EXISTS (SELECT *
              FROM Customers
              WHERE Customers.customer_id = Orders.c_id
              AND Customers.lname = '4');

At first, I thought this delete query will delete the whole table as EXISTS returns TRUE(I mean, there IS a row with customers.lname = '4') But here is the result:

subquery returns True?? and the row with lname = 4 is deleted.
So I expected update query will update the row with customer_id = 401 like it just did for delete.
But here is the result :

UPDATE Customers
SET lname = 'aaa'
WHERE EXISTS (SELECT * 
              FROM Customers
              WHERE customer_id = 401);

Whole table is updated like EXISTS just returns True. This really confuses me. Why EXISTS works differently for delete and update? Or did I do something wrong(I think so, but I can't figure it out myself)? What happened to update query and delete query?

In the first query you are performing the exists check for each row as you are referring the source table (orders.c_id):

SELECT *
FROM Customers
WHERE Customers.customer_id = Orders.c_id
AND Customers.lname = '4'

while in the second query you are not and you have just a true or false condition acting as if block.