Do we have a single definitive original text of the book of Ruth? That is, in the original Hebrew / Aramaic? If so, how many words are in the original, and does this make it the shortest book of the Old Testament?
According to Word counts for every book of the Bible, which counted all the words of each book in the original language (and also explains how he got the data), Ruth has 2,039 words in the original language.
That's 19 more than Song of Solomon and also more than Joel, Malachi, Zephaniah, Jonah, Habakkuk, Haggai, Nahum, Obadiah, and Philemon. So no, it is definitely not the shortest book in the Old Testament.