Sorry, I missed that you were talking about stealer logs. This specific credential dump of 2B emails wasn't a stealer log, so stealer log info will not tell you anything about this specific credential dump.
You're right that the API for stealer log info isn't free.
However, the dashboard can provide you information about stealer logs for free.
Every other endpoint requires a subscription. This is very far from “The API is free”.
> searching by account wouldn't tell you anything useful
The API can return the domains listed in stealer logs for a specific email address: https://haveibeenpwned.com/API/v3#StealerLogsForEmail