How to achieve specific blurred spark-like particle effect in UI

Saw this very smooth blurred, fire-like sparks blurred particles moving across the screen in the Descent: Legends of the Dark unity app, and was wondering how you think they implemented it. As far as I'm aware, particle systems don't work in the UI canvas. How did they achieve such a smooth motion?

https://i.gyazo.com/ce23fd3d400523af91d4b6e1a3ddc864.png

https://www.youtube.com/watch?v=rBV36Uhz9gQ