That's a different kind of holiday. "Férias" is used for the days we take off from work or school (usually after a semester or a year), which you may call a vacation, a holiday or a break.
But the day on which business is suspended by law, such as a national holiday, is called "feriado". So we would say "hoje é feriado".
"The holidays are over" is more natural.
Actually, we use the expression "acabar + de" as an auxiliary verb when we want to say that something "just" happened. And that can be a problem when translating that something "just finished" or "just ended". In that case we usually use "terminar" as the main verb, since it has the same meaning. So "the holidays just finished" would translate to "as férias acabaram de terminar". Some people also say, colloquially, "acabaram de acabar", which sounds a bit funny.
I could use an explanation, please. In this lesson, the verb "acabar" is not/not followed by the preposition "de", and is/is conjugated in the first person plural past tense, so why does The Owl insist that the English translation is, "The holidays are over" (which is in the present tense) and does not accept, "The holidays were over". Why? Desde já, um grande obrigado.