So many many posters who don't understand what risk actually is and how to mitigate it.
Exactly. Nobody needs to know for certain what this man's intentions were - the key thing (pardon the pun) is the uncertainty.
So start with: my keys are missing, there was a male acquaintance I know little about in my house, he might have taken them, I don't know his intentions.
Then risk assess on the facts. Millions of women experience violence at the hands of men. It's more likely to be men you are acquainted with than random strangers. In England and Wales, two women each week are killed by partners or former partners. That's not hysteria, those are cold, hard facts.
So, do you do nothing and wait until the keys turn up? Risk he might be violent and have ill intents, moderate to low. Outcome if he does, the harm could be catastrophic. Multiply those two things and you're in the red/ amber zone on the risk register. Then it turns out that yes, he had the keys. You take a big step into the red.
It doesn't matter if your husband is lovely. It doesn't matter if most men are poor misunderstood little souls. It doesn't matter if someone accuses you of hysteria. Someone you don't know well enough to trust had your keys, so change the locks.
Hysteria would be running around with pitchforks tracking the man down with a posse. Sharing stories about times when men have been violent and aggressive, from stalking up to and including Ted Bundy, is not hysterical. It's just a fact. As Germaine Greer pointed out many years ago, most women would be surprised if they knew just how much men hate women.
Pretty much every woman I know who I have spoken to about this has had some encounter with a man who threatened them in some way, whether that be following them home or experience of abusive relationships. It's not hysterical to protect yourself from this very real risk.