Twitter is not the first to start collecting information on which app you download onto your phones. According to twitter, you have to opt out of the interest based ads.

I'm sure you knew about opting out, didn't you?

The whole point is that it will help twitter sell more, relevant ads to you, along with suggesting twitter followers, and, adding other relevant content into your time-line.

To help build a more personal Twitter experience for you, we are collecting and occasionally updating the list of apps installed on your mobile device so we can deliver tailored content that you might be interested in. If you’re not interested in a tailored experience you can adjust your preferences at any time (read below). Additionally, if you have previously opted out of interest-based ads by turning on “Limit Ad Tracking” on your iOS device or by adjusting your Android device settings to “Opt out of interest-based ads,” we will not collect your apps unless you adjust your device settings.Twitter To Collect Data On What Apps Users Install On Their Phones [support.twitter.com]