The point of using the term “sinophobia” rather than simply “prejudice” is that no, it does seem that some subset of people are uniquely unable to “criticize” PRC policy without injecting some trope about mainland Chinese people and culture. In fact, the point is to repeat the stereotype as if it were fact. The policy (whether it exists or not) is just an excuse.
For that matter, sincere requests for clarification are not immediately followed by attempts to dismiss the underlying concern as invalid. This inherently makes the request insincere.
If the criticism of the PRC were mixed in with Sinophobia, then doom2 should have expanded on that. As written, there's nothing to suggest that doom2 witnessed anything other than criticisms of the PRC. The idea that it's mixed in with stereotypes about mainland China would be a good example, but it's entirely your injection, not something stated in doom2's comment.
Remember, allegations of "dog-whistles" are really just saying "I'm assuming other people are implying XYZ." My conservative relatives think words like "diversity" or "inclusion" are dog-whistles for anti-white discrimination. They're earnest when they say the feel attacked, but that's entirely on account of their own assumptions and does not indicate any actual racism. If doom2 wants to make point, they should actually explain what they witnessed that was bigoted or hateful - don't just allege "dog-whistling" and do nothing to substantiate that claim.
For that matter, sincere requests for clarification are not immediately followed by attempts to dismiss the underlying concern as invalid. This inherently makes the request insincere.