Presumably because a lot of readers here use vagrant for development environments and may be interested in hearing about a particular bugfix in this release. That's why I clicked at least...
Sure it is, I love it and use it every day... but seeing something like this on the HN homepage makes me think something has happened I really need to know about.
The way it works is someone posts a link. If enough people for whatever reasons of their own decide to upvote that link, it makes it to the front page.
There's never any one justification or reason why something gets voted up. Everyone has their own reasons. One person may upvote because they find it interesting, another because they like it, another because they agree with it, another because they think it's important, another because they want others to know about it, etc. It's a never-ending popularity contest.
Software releases get posted here pretty regularly, and if they're popular enough or interesting enough to the segment of HN readership that happens to be online at the time they get voted up. Period. No explanations given or required.