It's not unlikely that at least some of them claim it was a mistake to avoid taking responsibility for their vote because they're aware of how unpopular it was. After being in parliament for at least ~5 years, it's hard to believe so many of them still haven't figured out how the voting works.
it's possible, but there are votes in different directions. It's also possible some just understood the question incorrectly or confused it with something else, not just "misclicked". Without knowing how often this happens in other votings it's hard to tell if this is unusual.
The only number I could find where between 2014-2015 [1], but in that year the average was 6.7 registered 'mistakes' pr. MEP. So it seems to happen quite often, I guess it only rarely has this big consequences.
[1] https://www.europaportalen.se/2016/02/svenskt-rostvelande-st...