A degree of pragmatic language impairment – inability to detect hyperbole/exaggeration/sarcasm/etc leads to responding in a literal manner to comments intended to be taken non-literally. Commonly associated with autism, but people who aren't remotely autistic can also display it when tired, drunk, stressed, emotional, using a foreign language in which they have imperfect fluency, etc. It is even more likely online, due to lacking other cues (such as tone of voice).

Because the statement it references is patently silly?