You have done damage to the person possibly quitting, and you have done utter damage to your own reputation.
It was not your business. It's his/her and the company's business to negotiate an appropriate cancellation period. And as long as both sides honor the laws in that regard, it's neither anything YOU can do or influence, nor is it in any regard your freaking business.
You do not even have proofs. You make a a joke of yourself. Or an asshole. It could be that the other guy has cancer or is burnt out, and in the utter need of a therapy. He/She might even be donating his leave days to not cause friction with the company targets. Or maybe his/her significant other currently is in the need of help on certain days; a newborn might be approaching, or significant other may need a drive to the distance university because of exams or tests.
What if the company starts interviews and even hires someone new, and it turns out he/she was simply going preparing for an upcoming Karate event? Now you have done damage to the company and to the newly hired guy who must now been told that all her/his other interview cancellations were waste! **
What is your benefit, really?
In no case, I can see any benefit from what you've done.
Congratulations. Just like YOU cannot be trusted, others can neither, and the story of a 100% "loyal" * careerist will now make it to the daily Corridor News.
Expect to become an avoided person in the future and not be told anything sensitive again.
Alternatively, but I hate to say, not even you has deserved it, you are now in the danger of becoming a target of bullying.
* Actually, you are the one illoyal, considering how you betray your coworkers.
** All mentioned examples are things I would not necessarily tell any random coworker.