This reminds me a lot of the tricks to turn BERT into a generative model. I guess the causal masking that keeps it to essentially be autoregressive is an important difference though. Kind of best of both worlds.
Masked language modeling has been compared loosely to text diffusion [1], so the paper's title claim may be loosely true in some sense even if it's misleading.
[1] https://nathan.rs/posts/roberta-diffusion/