What was the probability that one of JaneStreet’s alumni, Sam Bankman Fried, would use JaneStreet’s brand name to build up credibility and then pull off the biggest ponzi scheme in human history?
Unless you happen to have some evidence presenting unethical and/or immoral actions on the part of SFB and Caroline during their tenures at JS, it only shows that JS don't try be an oracle predicting future morality or ethics or judgement of their candidates for the rest of their lives.
JS aren't future tellers when it comes to their employees' lives after they leave JS, and JS has no control over those employees once they depart either.