I'm not particularly happy about that argument. It perfectly explains why complex organisms like bacteria don't suddenly evolve to its mirror image. But it doesn't explain why this hasn't happened at a much earlier stage in the evolutionary history.
We don't have multiple lineages of life in general. Everything is using 4 base pairs, roughly the same set of amino acids and some universally preserved genes. So there was a bottleneck where everything else was outcompeted.
So even if some mirror life chemistry was going on at some point, it just didn't make it along with all the other things that didn't.