Is it me, or does ‘hackaton’ mean ‘come and write code for us for free’?

Depends where you go. I’ve been to / organized a few where you own everything you build, and are encouraged to try make it a reality. Whole point was to advertise or promote a new cloud, tool, service etc.

And sometimes you pay them to write code.

We'll be hosting a hackathon focused on high schools next week. We're not keeping any code/projects created by the participants. The best projects will win money to buy a new tech and they're encouraged to further develop their ideas and projects into full commercial product in a small local startup accelerators.

So it really depends, which company is hosting the hackathon and for what purpose. If you are participating on a hackathon which is organized by a company as a competition to find the best scenario/usage of their product, you can't be surprised they want to keep the result.

Bigger problem for me is that 'hackathon' pretty much became buzzword. Everybody needs one (incl. our company) although the overall idea and purpose is often missing and the mngmnt is often unable to formulate anything more than 'hackathons are cool, so we'll do one too'.

On the other hand it's an opportunity to grab a part of a corporate budget, so we got ourself a shelf full of IoT toys and boards.