I am of course aware that the island is an island. It has been tagged as such in the relation you linked.

However I think the locality in the centre of the island can be considered a town. My reasoning is that people living on the island would give their address as one of the hamlets, then "Peng Chau". e.g. "Tai Wo Tsuen, Peng Chau, Hong Kong"

Currently if you do address lookups on Nominatim it gives the town as "Discovery Bay" which is certainly wrong.

I looked for other examples of towns on islands around the world before making the edit.