As far as I can tell from an slightly extended skim of this text, this is a case of people from an adjacent field (theoretical GR) writing a paper that finishes

As far as I can tell from an slightly extended skim of this text, this is a case of people from an adjacent field (theoretical GR) writing a paper that finishes with a remark about their abstract model that does not easily translate to the one used by the EHT. In fact, I find this rather nice summary towards the end of the article: "In particular, EHT’s simulations show all of the effects mentioned above; there’s none of this of which they are unaware. [...] Thus it’s not enough to argue the photo itself is ambiguous; one has to argue that EHT’s more subtle analysis methods are flawed. No one has argued that yet, as far as I am aware." To me this reads very much like "I probably shouldn't have used 'controversy' in the title".