Empirically, absolutely nothing. You can't judge the security of a software based on its marketing material.

But you can determine that nobody at signal has used or even seen an android phone.

I'm not sure why you would say something like that. The original TextSecure and Redphone apps were exclusively on Android until it got bundled into a single app and released as Signal on both platforms. Android is still often ahead, and seems preferred much of the time.

What? Signal/OWS seems to develop new features on Android first, and that animation up top is an Android phone...

It's not an Android phone. Android has either on screen Navigation Bar or Physical Navigation Bar not both.

What are you on about? You can enable on-screen buttons while still having physical capacitive buttons.

http://m.imgur.com/u5hcJYQ

Many 3rd party custom ROMs have the feature, including CyanogenMod, the most widespread open-source build of AOSP.

Not on stock Samsung phones.

So they made a screencast and blended it with a video of a hand touching a phone to avoid shadows and improve image quality. Is that really your takeaway from the article?