Twitter abuses an ios api to check if they can open a url with a specific app scheme. If the api returns true it means you have the app installed. You are looking at the list of apps that twitter checks.

This may be useful:

https://news.ycombinator.com/item?id=8665581

http://www.wired.co.uk/news/archive/2014-11/27/twitter-ads

https://support.twitter.com/articles/20172069