Functional vs Performance Requirements

"Performance Requirements are about criteria and meeting criteria, Functional Requirements are about describing how a system behaves."

I think I agree with  that statement.

So for example, a Performance Requirement could be:

The laptop shall withstand shock of 20g's (good laptop!).

The criteria we are talking about is shock. To verify this requirement, we would measure the end product against this criteria, and see if it meets it.

A functional requirement:

The add button shall sum the values in fields A and B and present the result in field C.

We are describing how the end product will function, or (in other words), we are describing the end product's behavior. To verify this requirement, we would exercise this functionality and observe the results.