The only assumption Yegge is making is that the Big Bang wasn't self-started from a confluence of previous state, but "initialized", overwriting that state, which almost makes sense: black holes overwrite later state, rendering incoming material arbitrary to its later states (they're an "information sink"), so why couldn't the Big Bang overwrite earlier state, rendering outgoing material arbitrary from its previous state (an "information tap")?
A variable is a piece of memory and always has _a_ value. The value may be arbitrary, the value may be unknowable, but we know at least one thing: that at any point in time a variable has exactly 1 value.
That said, even if we assume that the universe had no state prior to the big bang, we can postulate that state to be arbitrary, because it may be 0, it may be 1, or it may be both 0 and 1 at the same time.
If you buy certain flavors of string theory, you could say that we can only tell what's going on beyond our own 'brane, as our 'brane happens to be an embedded system that we would need to step outside to understand what exists outside of it.
Essentially it seems to me that Yegge is saying that we don't know what's going on outside of our 3-space 1-time universe, and that even posing the questions from within the universe is an exercise in futility.