The pillar is fiberglass too, I believe.

There's a (mostly terrible) documentary about a previous bansky "statue" deposited in London that, in one of its better moments, tracks down the people who actually make statues for artists like banksy.

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

edit: I feel I should clarify that this is not an official Banksy documentary. He made "Exit Through the Gift Shop" which is an amazing film which I highly recommend to anyone.