So what actually happened to cause 400+ votes on one poll?
Great question! And the answer is, well, we don't know.
The ball theme poll from earlier in this year almost hit 400 itself. A lot of people have expressed amazement about it, and even suggested it may have broken containment out of the FTC. I wouldn't be surprised! Despite the event being fantrolls only, we do still tag major posts with the main homestuck/hiveswap/friendsim tags and do still get canon character blogs and non-roleplayers interacting with our posts.
Tumblr polls only have one requirement to vote and that's to have an account and be signed in to do so. All 400+ users who voted on the poll had, by it's very nature, to have an account on tumblr.
I assume you sent this ask because you're suspicious of this amount. I won't tell you how to feel! Your feelings are yours. What I will say is that if anyone suspects and has evidence towards a possible conspiracy to pack the votes or behind the scenes campaigning then I implore you to please reach out to privately with that evidence so we can take action.
Until a scenario like that crops up, we intend to leave the results as is as we have nothing that points towards otherwise than a high number poll turnout similar to the ball theme voting poll.