Quantum fluctuations, as far as I know, are mini violations of the conservation of energy (ie creation of virtual particles that can exist for short time periods). If space-time has a rest energy of zero (which me must assume, otherwise.. there is no explanation for how life could exist in what would be an intensely dense, unstable and hot universe) then it would follow something as tiny as a quantum fluctuation could be causal for an inflation. The problem is that it's all speculation right now. 😛