If someone who has the skill to hack Canon's site and did only that much, he/she was an idiot.
(i.e., your conspiracy theory is way too farfetched.)
Oh no, they wouldn't be an idiot at all. Quite the opposite. In many cases hackers will make only subtle changes to a web site, sometimes just enough to cause disruption but also not cause immediate attention so their work lingers longer. This is not a theory, it happen often.