I'm not sure what people think comments like this accomplish. Americans aren't super gung ho about America. The great universal American past-time is criticizing America.
China is the #2 economy in the world. America is constantly whining about the #1 economy in the world, why would they not also whine about #2? The truth is that there's nothing unique to Americans complaining about China. A lot of what Americans complain about China is quite similar to what they complain about America. This is especially true with authoritarian sentiment, with the fear that China will be the model used for the US against themselves. Yeah, there's a few "fuck China, America best" but I'd be shocked if the was anywhere near the mean or average sentiment. People are more complicated than this and Americans are just vocal about everything. Because they're so vocal, it is easy to ignore some things and pay attention to others, especially when they validate your internal biases (such as complaining about your country, which is nationalism).
I think it's the broad, off-topic, pro-China/anti-US comments, like this that make people feel like it's probably a bot or human equivalent.
If the post was actually a reply or rebuttal to any of the comments content it probably would give that vibe.