This is not a god argument, there might be natural processes that can trigger such events.
We really don't. We don't have any physical evidence of anything from before the big bang (presuming that's what we call the "beginning"). Zero. All we have is people having views on the current situation, trying to apply those views backwards to "before", where they may or may not fit, and saying "I think it's like this".
You could - hypothetically - pause the computer, check its state, change a few variables, and the simulation would experience instant modifications.
A slow simulator could take many "real" time units to calculate each in-simulation time frame - and this would be invisible in-simulation.
And so on.
You have a fully causal system, but the simulation is ruled by its own independent emulation of causality.
Of course a computer implies a conscious user. But let's attempt some wild speculation and suggest that a "simulation" could also be a completely natural process - something that happens in a much bigger causal substrate: a kind of causal symmetry breaking, where a subset of possible relationships crystallises out of a bigger set of possibilities and then continues independently, losing some degrees of freedom.
A simple two level topology is the simplest possible model. But "causality physics" could allow all kinds of topologies - nested, circular, fractal, etc.