This is the 9357th most frequent Japanese word.
短かっ
"短かっ" is the stem of the word "短かった," meaning "was short" (past tense of "short").
Here, "短かった" is used as the past tense form of the adjective "短い" (short) describing the explanation length.
彼の説明はとても短かった。
His explanation was very short.
In this sentence, "短かった" describes the duration of the trip, indicating that it was not long.
旅行の期間が短かったので、たくさんの場所に行けませんでした。
Since the trip duration was short, we couldn't visit many places.
"短かった" here reflects the comparison of the game's conversation duration against expectations.