Speaking as a professional video editor, it appears they did what’s called a “morph cut” in Adobe Premiere Pro. Essentially, it’s a transition used to combine a jump cut/two separate takes to make them appear as one. It could also be used to remove parts of “talking head” footage that aren’t wanted — for example, if the subject is saying “um” a lot and the editor wants to get rid of it, while still maintaining the illusion of one fluid shot.