Would they? The XZ utils backdoor was only discovered by what can only be described as an insanely attentive developer who happened to be testing something unrelated and who happened to notice a small increase in the startup time of the library, and was curious enough to go and figure out why.
Open does not mean "can't be backdoored".
A very bizarre rise in the polls indeed. A mere two weeks ago he was polling at barely 2%, in the exit poll he came third and instead he's first. People expected Simion to be the far-right candidate but he was well off.
Ciolacu still has the best cards, ahead in every poll in 1v1 matchups (and his lead mostly grew over time). But as far as I can tell there hasn't even been a poll of just Ciolacu vs Georgescu, because nobody expected him to get remotely close to qualifying for the second round.
Hopefully Ciolacu manages to win regardless.
EDIT: Lasconi is the second candidate, she beat Ciolacu by just 2700 votes. She is also pro-EU and pro-Ukraine, so foreign policy-wise they're not much different it seems. Good luck Lasconi!