Why does he said "there" instead of "this"?
It's common to use the expression "there is [x]" when presenting something to someone. It holds the same meaning as "this is [x]," except the "there" also helps to add distance between the speaker and the item, and to draw the item and another person together. We can understand the host as using this expression to present the figure to Tom Holland and make him feel a closer connection to it. Ex: There's your coffee. It's ready for pick up. Ex: There's your cat walking down the street.