I will say that anytime I have come to finish a job for another handyman/homeowner, it seems inevitable that something will have to be taken down and redone. Especially with drywall.
Did he mention that he wants to do this just because it doesn't butt into the ceiling board? He may have other concerns, such as too many joints/improper use of crush edges, IE more work for him mudding.
My first guess is that he is more worried with the finished product and having a job going smoothly than creating more work and money for himself. It's never preferrable to be finishing someone else's job, for now your name is on it.
I always start with the ceilng first, just nice to have that extra support, IMO, probably less chance of cracking in the future.