Learn Russian: На кинофестивале мы встретили номинанта Квентина Тарантино. - At the film festival, we met the nominee Quentin Tarantino.

This is a key rule for foreign names. Foreign first names ending in a consonant, like Квентин, decline like standard Russian masculine nouns (taking the -а ending for the animate accusative here). However, foreign surnames ending in -о, like Тарантино, are indeclinable. They never change their endings, no matter the grammatical case.

Why does the word for festival, кинофестивале, end in -е and not -и?

It is easy to mix this up because words ending in a soft sign (-ь) can be masculine or feminine. Кинофестиваль is a masculine noun. In the prepositional case, masculine nouns ending in a soft sign take an -е ending. You would only use an -и ending for feminine soft-sign nouns, like площадь (square) or ночь (night).

Why do we use the perfective verb встретили rather than the imperfective встречали?

Here, встретили describes a single, completed event: you successfully crossed paths with the director. If you used the imperfective встречали, it would change the meaning from accidentally bumping into him to the ongoing action of formally welcoming or receiving him (for example, if you were the festival staff greeting guests).

Why are номинант and Квентин taking the genitive -а ending if they are the direct object of the verb?