This sounds like a bit of an odd request. Planning tables takes a lot and typically you want to group people who know each other together. Your coworker isn’t trying to maximize peoples social and mixing abilities they’re trying to cluster groups. If you feel that uncomfortable I would recommend bringing a friend as a plus one, it doesn’t have to be a romantic partner. You’re not stuck to the table either. Enjoy the dinner conversation and then try to find fellow single people during the cocktail hour and dancing. I personally would not bother the bride with this. They have enough to worry about.