Reasons, and those reasons may be crap. But I struggle to see how them explaining to him what they want or want to change is dishonest? To me something can be completely honest and be crappy, as this situation very well be.

People say all the time they want honesty and in this case it seems to me the boss was honest. And OP can now respond to the different workload/dynamic - this seems far better than just having a bunch more work heaped on him with no explanation why or a chance to respond? (Which he said he strongly did)