@Arminius accidental comment above ^
I do agree that there shouldn't be any implicit requirement to pay em out. Especially with what they've said about the vulnerability details I'd have to assume it was a small severity issue that wouldn't justify a large bounty. That being said there's no implicit requirement for the bug finder to offer bugs to the company as long as they're not selling/publishing the vulns. Both sides are looking out for their best interests.