[stupidcar]

That is just how these interviews are done by the BBC. It would be the same if both participants were in the UK speaking English.

I think it's perhaps because the BBC does a lot of educational material aimed, at least partially, at children and schools, and the presenters are trained to be very exaggerated and enthusiastic in their reactions. Experts like scientists and engineers can be quite placid in their delivery, and so the presenter's job is to make whatever it is they're talking about seem more "exciting". E.g. some engineering project, scientific experiment, historical fact, etc.