Hey @the_arnon the way this works is that the code is split and only resources need for that particular action are shown to you on Android instant. Technically you aren't downloading the app, you are only viewing a preview with the content that you selected. If you like what you see you can download the complete app.
eg) I want to watch a video on Techcrunch's app, but i don't have it installed, i click on the link from Google, android instant will load the code for that particular segment (i.e the video) in the interface of the Techcrunch app , as i interact with the video and scroll more parts are loaded. Once I'm done i hit back and I'm back to Google.
Its something different and i can't wait to see what people build with it.