You've misunderstood. The blog post is not talking about running random binaries. It's talking about opening links and files using different programmes, like PDF viewers, video players, etc. There's a video of a talk that the developer gave, which I can't find the link to at the moment, where he demonstrates running a map programme (already installed on the machine, not just fetched from a random website) to open a link with lat/lon coordinates with an interactive map.

In general, Dillo follows the Unix philosophy. You use separate programmes to handle things that Dillo can't itself, like watching videos.