Did they say anything about the cause?
No they didn’t. They said it occured on the western side of the island. Maybe it’s for the same reasons California experiences some of theirs.
Guessing: rains and melting snow over-saturated the cliff soil.
My guess is that it is related to this:
The Quick Clay Landslide at Rissa - 1978 (English commentary)
https://www.youtube.com/watch?v=3q-qfNlEP4A
The soil type has a nasty habit of becoming easily liquified.