I don't know what constitutes an "adversarial statement" in your region of the world or what consequences such a statement has. But I can tell you why the executive is so angry about what you said or wrote:
Developers need to be informed the scope, timelines, and other expectations that are material to the success of needed changes.
This is not a statement of fact. As such, it would be blatantly false. Developers can work without those, it's just that the quality of their output will degrade significantly. What this is, is an order. It needs to be done, no alternatives. The correct answer to that sentence would be "Sir, yes, sir!"
Lets try this again being less commanding:
Getting information about the scope, timelines, and other expectations that are material to the success of needed changes will significantly improve the developers output.
And maybe if you want to insist:
To meet the given deadlines and quality standards, improving our output is necessary.
What is the difference? Well, in the first case, you took it upon yourself to play executive and already make that decision that improved output is favorable compared to the costs of getting the information across. Then you commanded your boss to take the decision you deemed right. The second version is taking the facts and giving feedback and leaving the executive decision to the guy that actually is the executive. Maybe it's worth the cost. Maybe not and the deadlines are too tight? Maybe something else altogether, hire more people, outsource, not take the project on, whatever else could be done. Making those decisions is the job of the executive. Not yours.
The point is: you played boss. You tried to boss your boss around, tell them what you need done instead of telling them what options they have. Bosses don't want to be bossed around by their reports.