This assumes that the ones who decide to vote in the EU election are a random sample of the ones that vote in the national elections, which is almost definitely not true. One of the parties is likely being over/under represented at the EU election.
>The more local the more people care but half of the population voting is not really drastically different than 2/3 of the population voting.
And I was simply pointing out how the result is different. I thought you were referencing that it was a random sample. Though apparently you just decided it's the same even though you knew it wasn't a random sample.
While for European elections it is usually 40-50% with huge differences by country (https://results.elections.europa.eu/en/turnout/)