This probably the most likely explanation.
Dorsey may feel he's simply not ready to be the OC for the Bills and needs more tutelage/supervision from Daboll.
If he goes to NY, he can continue to learn and get support from Daboll. If he stays in Buffalo he'll be on his own with very little support.
The expectations are far less in NY as well as Daboll will have at least 2-3 years to turn the team around.
If Dorsey stays in Buffalo and the Bills go 9-8 and miss the playoffs, he could get fired after 1 year.
The safer choice is to go to NY.
The bolder choice is to stay in Buffalo