You are correct, some know what they are talking about. But there are also many people who think that being a smart person in one field makes them a smart person in every field. It is disrespectful, it implies that they think their field is easier than yours and it must not be that hard to figure out. It is also very easy to spot.

I did not mean to imply that everyone is one-dimensional, I personally have professional experience in the finance and software industries and have respect for the people in them. But when some finance expert suddenly becomes an opinionated epidemiologist I call bullshit (a random example that has happened far too often the past few years).