Just a speculation, but I think that his reaction is more to the media rather than antis on social media. Yuzu is of the internet generation that is very aware of the hate culture online so it is hard to believe that he would let that get to him, especially since there is more support than hate for him online anyway. The media on the other hand represent the public opinion (or so they claim), so when something hateful or fake is published and later spread and discussed on social media, it is easy to believe that this is what most people in Japan think and we had some discussions here in the past about that as well. There were also things published quoting (or are written by) people who Yuzu knows and most likely respects that were unkind and sometimes even mean, those would be more painful for him to read than what an unknown person on the internet would say.
Most importantly, we need to remember that Yuzu was in a very stressful and difficult situation last year with the Olympics, injury, expectations, and the high level competition, which can make anyone more susceptible to negativity. His struggle while worrying is quite natural and it is a very good thing that he is talking about it publicly. This is a sign of recovery and renewed strength, and it shows that he is taking a proactive stance by addressing the issue rather than hiding from it or burying it. So I would not worry too much, I think he is in a good place right now