From my perspective, there are a couple of scenarios (that come to my mind as of now) where the need of having multiple accounts is justified and understandable
You missed a scenario that comes down to Bitcointalk being as free as possible, and offering free speech:
If you're hesitant to say something controversial because you don't want it to be associated with your name, please create an alt account and say it.
(but always with transparency regarding it)
As shown above, theymos disagrees.
I support the forum mission of being as free as possible as I have stated previously on my posts. I was just providing some rationale (from my perspective) of what could motivate the use of multiple accounts, I am sure that there can be others (and more depending of one's perspective).
While I agree with LV
general idea, it's also true that, strictly regarding this contest, there really is no rule preventing PytagoraZ from being eligible. This, of course, is not pointing the finger at you, but an observation... We can only learn from such incidents and better the set of rules in time. Same happened with BCA during years and also with other similar events. It's really impossible to anticipate everything what can happen the future, what a particular user may do or try... so we can only adapt to the situation.
I wasn't aware that similar events happened with BCA. If I do run next year edition more feedback will have to be gathered in order to reach a set of balanced rules I guess...