Explanation

The nested function includes an assignment to this variable, and the variable is not

Listed as an input or output variable in the nested function definition
Listed as an input or output variable in the parent function definition
Assigned a value in the parent function

If there is a function on the path with the same name as the variable, MATLAB interprets the variable in the parent function as a function call. Otherwise, the variable is shared between parent and nested function. This code might result in unintended behavior.

Suggested Action

To clarify which behavior you expect, modify your code.

To share the variable between the parent and nested function, assign a value to the variable in the parent function.
To use the function on the path, rename the variable in the nested function if it has the same name as the function.