Your boy was in an unfamiliar place, likely after a car ride, when he went on the date. So he may not have been acting as he normally would. The fact that they seemed to get along OK during the date is a good sign, but that doesn’t mean they will be best buds right away.
What is the neutral territory? The bathtub? Did they spend some time getting used to each others’ scent first? If not, then it might be a good idea to take a step back. Maybe do some stuffed toy or litter box swapping to get them used to what the other bunny smells like. This can take some time, so don’t rush it. When you start bonding sessions again, there are some things you can do if there is still fighting. For example, you can put them in a box together. If they try to fight, shake the box a bit to break it up. Not enough to hurt them or anything, just enough to get their attention/interrupt them. Or you could try a car ride together. Sometimes the stress of the car ride makes them forget about fighting. Just have someone next to them to break them up if they do start fighting. There are some other techniques too. Those are just a couple of examples.