If this had happened during the actual exam, that might be worth nothing. Given that it happened during the writing sample, which is essentially worthless, it's not worth worrying about. Just be happy it didn't happen during the actual test.
P.S.: Writing Sample =/= Essay =/= Personal Statement. It is only used to ensure you don't drool on the page, and (rarely) to make sure you actually authored your personal statement, by comparing writing style.