While I appreciate the school yard knee jerk response of 'No, you're the one with the basic empathy disconnect, stoopie head!', this is not a case where it applies.

I can describe the actions of someone as a 'basic empathy disconnect' while at the same time being able to empathise with them - in this case understanding that these people are seeing the outpouring of grief you describe, being confused by it as it doesn't align with their feelings, and then feeling uncomfortable because they seem out of step with what 'everyone else' seems to be feeling (which is not a laughing matter; social rejection is hardwired to be super distressing for humans). these feelings influence them to make a secret post about how they 'don't get it', both expressing their frustration and also looking for social validation in the form of people saying they feel the same way.

Whereas, if some of these posters had taken a second to reflect, they might have realised that the people expressing sorrow so visibly just had a particular emotional connection with the celebrity or their artwork that the secret posters might not share, but might be analogous to some other emotional connection the secret poster has to something different. So, you know, a basic empathy disconnect.

('Basic empathy disconnect' i.e. an instance of not being empathetic =/= 'incapable of empathy', fyi)