An interesting control would have been to flip a single bit but also flip a single char so that it flips several bits and compare the results.

edit: Reading the linked article, they describe one of their validation method: > The Host header contains the domain the HTTP client resolved to connect to the bitsquat server. If the Host header matches the original domain, the corruption occurred on the red path (DNS path). If the Host header matches a bitsquat domain, the corruption occurred on the blue path (content path).