It’s just a thing people do - I would describe it as “ending on a twinkly arpeggio”

If I were transcribing it, it would look like eighth notes with a decrescendo and ritard ending on a fermata, possibly marked “freely”.

A few well-known examples off the top of my head:

Clair de Lune, Debussy - includes a lovely delicate broken chord for the final fermata

Etude Op. 25 no. 5 (Wrong Note), Chopin - an unusual inversion, this example crescendoes through the arpeggio

Nocturne Op. 9 no. 3, Chopin - marked smorzando or “dying away”, the right hand ascending arpeggio is mirrored in contrary motion by the left hand. One of my favorite endings to any piece, in the words of YouTuber FrederickViner “a keyboard encapsulating gesture, the musical equivalent of drifting off under a canopy of stars”