A pure function can even change data member’s value?

Question

-This is what I have read in the document: “Pure Functions promise not to modify state or the members of the class in any way”.
( https://docs.unrealengine.com/4.27/en-US/ProgrammingAndScripting/Blueprints/UserGuide/Functions/#:~:text=Functions%20can%20either%20be%20Pure,just%20output%20a%20data%20value. )
-But the simple example in the picture show that a function marked with pure can even change the member value and give no error ; Am I missing or misunderstanding something ?