Judging from their other infrastructure talks its far more likely they are shipping the application in a container to Apache Aurora, and having the process managed by Mesos.
I can't remember if all their services are now running on Mesos, but I'd bet their newer ones are.
Did they add a layer between their backend and mobile to pre-render the page server side, or did they get rid of their whole scala/jvm stack to replace it with Node?
My guess is they have a front with Nodejs for mobile.twitter.com and behind that you have all their scala/jvm microservices. Recoding all their microservices would be way too expensive. I don't think they use Nodejs for their RESTful API but I am curious to see more about that. Uber uses Nodejs for their GPS API so who knows...
Most likely they include a bit of Server Side Rendering using the same templates they have in their compiled asset. Actually getting to share code here would be a pretty big win.
I remember seeing Twitter switching from ruby/rails to the JVM for a lot of their backend a few years ago. I wonder why they're using node now (unless the mobile traffic was never moved to the JVM)?
[2] https://github.com/Unitech/pm2