You Don't Know What You're Talking About

Trying to discredit a Target by questioning things they say or do (or write) in a critical way is a common Control -domination-bully behavior. A person needs to believe first that they are innately superior to the person they're targeting, and must also believe that they are more knowledgeable, experienced, smarter or wiser than the other person.
"Where did you hear that?!"
"I don't think that's true."
"Where are you getting your information from?!"
"What did you just make that up?"
"Who are you supposed to be, an expert?"
"What makes you think you know what you're talking about? You don't even have a degree!"

Because controllers and people with narcissism are often fixated on finding ways to "prove" that they're superior and that others are inferior, wrong, and don't know what they're talking about, they tend to "interrogate" other people about pretty much any subject, and imply or accuse them directly of "Not knowing what they're talking about" or "Not knowing what they're doing". They won't have a discussion or ask questions, they'll just do THAT.

It's like how some humans will just lumber in and attack a random animal with a stick without knowing anything about the animal, and without making contact with it first, just because it's "there".

There's no "reason" for this behavior except for the person's own behavioral and emotional issues.