I reconsider my first answer. Although I still don't recommend confronting the offending diner:

Why has the restaurant seated you so close? At three hundred dollars a table, the OP is entitled to better. (I am assuming that there was space in the restaurant to keep people farther apart.) So, in a case like this, ask to be moved. And consider not going back to that restaurant if they did seat two tables adjacent to each other and leave a lot of space in the rest of the restaurant. If that was the case, that was amateurish on the part of the restaurant.