Comment by kelseyfrog

If you read the paper, you'll find "More Expressive Approximate Posteriors with Normalizing Flows" is in the methods section. The authors are in fact using (inverse) normalizing flows within the context of VAEs.

The appendix goes on to explain, "We apply simple volume-preserving normalizing flows of the form z′ = z + b(z) to the samples generated by the encoder at each level".