It's a smart move, and as he said he's taken the time to think about his response.
The prize is under no obligation to shortlist him anyway - he could have just not been shortlisted and we'd never know if it was because of what he said.
He said he'll do this if all the flouncers return. That's unlikely but if they do he'll have made a massive, yet very peacable win - promoting the idea that people with differing views and perspectives can take part in literary life and celebrations together, and put witch-hunting and cancellation behind them. They also return to the chance of a prize (a better chance if he removes himself) as a reward.
If they don't all return, they are showing they value cancellation above reconciliation and reward, and he has a good chance of being shortlisted and winning - which they don't want.
Meanwhile whatever the outcome he shows everyone what "going high" looks like - generous, thoughtful, no threats, no nastiness, no greed, kind and encouraging to newer writers even if they disagree with him.
Well played JB.