It tells you that an address in your domain has been included in a breach. It doesn't tell you which address was included. That's what the OP and I are opining about.
Edit: When I try to do a domain search I get told:
> Domain search restricted: You don't have an active subscription so you're limited to searching domains with up to 10 breached addresses (excluding addresses in spam lists).
My domain has 11 breached addresses.
But I think you are right, because I only have 3 breached addresses under my domain (I do see the 10 addresses wording under subscriptions)
I understand, but it's frustrating.