It looks like GitHub Pages is serving files from your site (for instance, http://morenoh149.github.io/app/ is an html file with a single paragraph element) but it's not serving them properly with all the Jekyll magic.
It turns out that GitHub Pages will override the source
setting in the config file. This means that while you've specified source: app
, it's looking at your top-level directory for content.
The solution is to move the contents of your app
directory into your top-level directory.