I’m not a wefwef contributor, but I’ve looked through their repo. (I’m also unfamiliar with capabilities of Android PWAs, although a brief look indicates that haptics may be possible on PWAs in Android.)

technical: wefwef appears to be using Ionic Framework to build the PWA. This can integrate with Capacitor to make a native app hosting the PWA, allowing certain native calls from PWA -> host OS, such as triggering haptics.

non-technical: Yes, but it won’t be possible in the PWA: devs will need to package the PWA as an app for App Store / Play Store, and also add some new code to enable haptics.