Progressive Web Apps may look and act like native Windows apps, but they're really just a way to package up content from a specific web site, like Twitter in this case. A company blog post explains that this new release is a way to commit to Windows, and "is part of a longer-term strategy to reach greater feature parity to all of our platforms." The team also promises additional features like night mode in the coming "weeks and months." Previous versions of the Twitter app will no longer be supported starting June 1st, so you'll want to update to the new PWA soon.