What I love most about this is that there seems to be some form of nominative determinism at play here because the surname of the original owners is Sizeland, which doesn't take a big leap of the imagination to connect to their owning an island of notable size. At the very least, Sizeland is definitely an aptonym.

https://en.wikipedia.org/wiki/Nominative_determinism

https://en.wikipedia.org/wiki/Aptronym