Its pretty common to be that level of knowledgeable. A lot of people are casually interested enough about animals and biology to have heard discussions about muscular structures that they can determine when something doesn't work. It doesn't mean they can form their own hypothesis on what a spinosaurus skeletal structure is used for, especially if he knows that even experts are still arguing about it until today.

It's wiser to trust the words of someone who knows his own limitations and admits to it than someone who confidently uses a word without knowing the meaning. You can't seem to grasp that people can have a varied level of knowledge about different things within the same subject.

You're basically saying that someone being confident about your car having a puncture is being paradoxical if he also doesn't have the confidence to say what punctured it.