While one shouldn't make any assumptions in any particular case, some people state Social Anxiety for 'further unstated reasons'. Such as being Closet-Trans, Closet-Nonbinary, Closet-PTSD, Closet-Hypervigilant, a Survivor, Autistic, Neurodivergent in some other way, or Currently Bullied elsewhere.
Reasons for doing this include safety, privacy, not being Out, or other situations often being more stigmatised than Social Anxiety is.
Systems aware of and useful for Social Anxiety can be set up somewhat more generally so as to be useful to Closeted people. (And partially Closeted people, who would e.g. state they are Nonbinary under some circumstances but find it easier to state Social Anxiety.)