It couldn't have been an honest mistake, they must have blocked it for political reasons. Imagine living in this state of paranoia.
They missed their chance though, because after that election the candidate in question tried to appeal to everyone by being so ambiguous that instead made everyone not trust her anymore (for example spousing communist policies and at same time choosing the richest banker in the country as vice-president).
This always happens in single vote systems. Any options who draw from the same subset of voters will divide the vote and weaken their own, and one anothers, chances of success. It's one reason many countries have a few large parties, with internal "subparties" rather than lots of seperate parties that differ only slightly.
Ranked choice voting solves this problem beautifully. It's a real shame it's not widely used for elections.
This means that the "vote division" thing is not really an issue... If you end in second place, you still get a shot to get all the votes of whoever doesn't want to vote for the first place.
Thus basically any candidate in second place trying to campaign saying the vote will be "divided" is basically bullshitting the voter base in an attempt to secure his second place.
The first place DO want to concentrate votes though, if you end with more than 50% of the votes (and Brazil has mandatory voting, so basically 50% of voters) then you win outright, so sometimes parties DO attempt to do this by pooling all their votes toward one candidate (for example several xxx-wing parties choosing only one candidate among them all and campaigning all of them for that same guy).