You have it plain sight. Refusing to engage with someone is not gatekeeping. Your definition pretty much aligns with what I said.
And if someone doesn’t have any idea what they’re talking about, then maybe they shouldn’t take part in the talking. You can’t tell me that you‘ll take cybersecurity advice from someone who saw a movie about hacking.
Which doesn’t mean that clueless people have nothing of value to add, but it’s unlikely (especially in highly factual discussions).