So a couple of thoughts here (thinking from both sides here as I don't know if there's a "correct answer" here per say):
1. If a person is saying bad things and committing demonstrable harm, in public, and that person wants to be a physician, then said behavior should be reported. I wouldn't say you should send it to adcoms — for reasons above, you may not be believed — but people (including non-med students) can and have been suspended and even expelled in some instances for racism or posts on social of such in the past. Similarly, if this person currently works a job, you could send said evidence to their employer. If this person puts this stuff on their social media profiles then that makes it more obvious. I'm sort of thinking of it here how my med school would police such behavior as part of our expectations of professionalism — it's for similar reasons that we're expected to report any instances of academic misconduct that we're aware of. That being said....
2. For the reasons listed above, if this person actually believes what they're saying, the mask will fall eventually. It may not fall now, it may not even fall in residency apps, but it will fall eventually. The truth of the matter is that no matter what, there will always be terrible people who apply to, get into, and graduate from medical school in any given year.
I'm not quite sure what I would do in your shoes, but unless this person happens to attend your university and/or work at your area of work/volunteer where you volunteer, I'm not sure you have much ground to stand on if this was just in a private chat with no verifiable background. I think I would probably just sit back and not do anything at the moment, and then IF somehow you end up attending the same medical school as this person and said behavior continues, then you have a much stronger ground to stand on.