With over 700Billion in assets - this is a pretty big bank. I think this is just a polite tweet - nothing more... so yes, for now I'm pegging this as absurd!
It's not just a big bank. The Commonwealth Bank was actually Australia's central bank before the establishment of the Reserve Bank of Australia in 1960, and was not fully privatised until 1996. They've also been well aware of Bitcoin for quite some time now. This is big news.