You could vent the LOX. "Venting" the kerosene would just mean dumping it all over the deck. That doesn't seem like an awesome option... My guess is there was

You could vent the LOX. "Venting" the kerosene would just mean dumping it all over the deck. That doesn't seem like an awesome option... My guess is there was 'plenty' of propellant left (to use a technical term for quantity...). The rocket could have flown back to the launch site, but they weren't able to get environmental clearance. While they may have adjusted the trajectory to take advantage of the downrange landing (letting the first stage burn longer), they wouldn't have had any reason to skimp on the propellant left over for landing, so I'm sure there was a healthy margin left in the tanks. More than enough for an impressive fireball.