It's not a bonus. It's payment for services rendered. They offered $10k for a service. He performed the service.
Say I take a cab home from the airport. The money I give the cabbie upon arrival isn't a bonus -- it's payment for services rendered. (The tip is the bonus.)
You guys can both be right and it still doesn't matter. If you're going to offer bonuses or incentive comp of any sort, plan on paying them. You should be allergic to any reason for not paying short of "there is no credible claim to being owed this bonus".
It's definitely true that bonus programs are usually intended for existing employees. Concrete example: my last employer blew out their numbers the year I left the company; I wound up in a 6 month transitional role (and a few additional months of outside consulting) after a cordial mutual understanding that I was going to leave. The whole company got a massive bonus. I got a negligible bonus, even though I was a full-time employee, and even though the bonus accounted for multiple years where I was a full-time, fully performant employee with no stated intention to leave.
Am I mad? Nope! Most of the (unstated) point of the bonus was employee retention. I was unretainable. Paying me a giant bonus was irrational.
I think that's the same sentiment 'cletus is talking about, and to that extent, I'm totally with him.
But the answer to most disputes about bonuses should generally be "I'm sorry we let this escalate to a dispute, it's important to us that everyone knows we deal fairly with the team, and so we're paying you the bonus. We wish you the best."
"Most of the (unstated) point of the bonus was employee retention. I was unretainable. Paying me a giant bonus was irrational."
This is why I feel _some_ sympathy for Miso - they've got a scheme intended to improve retention. They then put in a set of requirements, goals, and milestones that didn't provide appropriate incentives for the behaviour they wanted to promote - they _weren't_ looking to reward guys who were going to bail after 12 months for hooking up their friends who were going to jump ship in 7 months. But they chose a set of metrics that means the OP had every right to feel entitled to his $10k.
But Miso have handled it _very_ badly (on the assumption that the blog post is an accurate reflection at least of how the poster saw the situation unfold).
If I could upvote your last sentence several more times, I would…
Say I take a cab home from the airport. The money I give the cabbie upon arrival isn't a bonus -- it's payment for services rendered. (The tip is the bonus.)