This point is somewhat controversial. I think many people has been disagreeing with this point and it all boils down to our definition of risk. I think there is no investment with zero risk and not bitcoin investment. We all agree that you have low chances of losing on the long run, but it doesn't eliminate in totally the risk of investment.

It doesn't necessarily mean that bitcoin price is going to zero. But bitcoin might be so low when you need it most. Your wallet could be hacked and leave you bankrupt. So, in as much as it is investment, there's risk associated with it.